Borussia Dortmund striker Sebastien Haller left the team's pre-season training camp in Switzerland on Monday after a tumour was found in his testicle.
The Ivory Coast international joined the German club earlier this month as a replacement for Erling Haaland, who has signed for Manchester City.
"In the course of intensive medical examinations, a tumour was finally discovered in the testicles during the course of the day," Dortmund said.
"During the coming days, further examinations will take place in a specialised medical centre," they added.
Dortmund paid Ajax €31 million ($31.5 million) for the 28-year-old after he scored 47 goals in 66 appearances for the Dutch side after joining in 2021 from West Ham United.
His 21 league goals in 31 games saw him finish as top scorer in the 2021/22 Eredivisie as Ajax secured a record-extending 36th title.
Haller also etched his name into Champions League history, scoring in all six group games - Cristiano Ronaldo is the other player to have achieved that feat - and became the fastest player to record 10 goals in the competition.
"This news today came as a shock to Sebastien Haller and to all of us. The entire Borussia Dortmund family wishes Sebastien a full recovery as soon as possible and that we can hug him again soon," Dortmund's sporting director Sebastian Kehl said in a club statement.
"We will do everything in our power to ensure that he receives the best possible treatment," he added.
Dortmund's first game of the new Bundesliga season is against Bayer Leverkusen on August 6, eight days after heading to third-tier 1860 Munich in the first round of the German Cup.
100 notable summer transfers
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Perr Schuurs - Ajax to Torino (£8m). AFP -
Paco Alcacer - Villarreal to Sharjah (loan). Getty Images -
Matheus Nunes - Sporting to Wolves (£38m). AFP -
Tanguy Nianzou - Bayern Munich to Sevilla (£16.9m). AFP -
Alan Virginius - Sochaux to Lille (£3.8m). AFP -
Thilo Kehrer - PSG to West Ham (£10.1m). Getty Images -
Pervis Estupinan - Villarreal to Brighton (£15.1m). Getty Images -
Destiny Udogie - Udinese to Tottenham (£15.1m). Loaned back to Udinese. Reuters -
Sergio Gomez - Anderlecht to Manchester City (£11m). Photo: Manchester City -
Alex Collado - Barcelona to Elche (loan). AFP -
Remo Freuler - Atalanta to Nottingham Forest (£9m). AP -
Marc Bartra - Real Betis to Tranbzonspor (undisclosed fee). Getty Images -
Giovani Lo Celso - Tottenham to Villarreal (loan). Getty Images -
Cheikhou Kouyate - Crystal Palace to Nottingham Forest (free). Getty Images -
Emmanuel Dennis - Watford to Nottingham Forest (£20m). Getty Images -
Nico González - Barcelona to Valencia (loan). AP Photo -
Luca Pellegrini - Juventus to Eintracht Frankfurt (loan). AFP -
Daniel Wass - Atletico Madrid to Brondby (£1.7m). EPA -
Pablo Marí - Arsenal to Monza (loan). AP -
Dries Mertens - Napoli to Galatasaray (free). AFP -
Jordan Veretout - Roma to Marseille (£9.3m). Reuters -
Christian Benteke - Crystal Palace to DC United (undisclosed fee). AFP -
Maxwell Cornet - West Ham United to Burnley (£17.5m). PA -
Georginio Wijnaldum - PSG to Roma (loan). AFP -
Lucas Torreira - Arsenal to Galatasaray (£5m). AFP -
Marc Cucurella - Brighton to Chelsea (£55m). Getty Images -
Ademola Lookman - RB Leipzig to Atalanta (£12.6m). PA via AP -
Renato Sanches - Lille to Paris Saint-Germain (£12.6m). AFP -
Riqui Puig - Barcelona to LA Galaxy (free). AP Photo -
Alex Telles - Manchester United to Sevilla (loan). AFP -
Carney Chukwuemeka - Aston Villa to Chelsea (£20m). Reuters -
Kasper Schmeichel - Leicester City to Nice (£1m). AFP -
Mattia Viti - Empoli to Nice (£10.9m). AFP -
Gabriel Slonina - Chicago Fire to Chelsea (£8.3m). Reuters -
Bernd Leno - Arsenal to Fulham (£3m). AFP -
Charles De Ketelaere - Club Brugge to AC Milan (£26.8m). AFP -
Joe Rodon - Tottenham to Stade Rennais (loan). AFP -
Borja Mayoral - Real Madrid to Getafe (£8.4m). EPA -
Cesc Fabregas - Monaco to Como (free). EPA -
Alexis Beka Beaka - Lokomotiv Moscow to Nice (£11.7m). AFP -
Marcus Tavernier -Middlesbrough to Bournemouth (£10m). Getty Images -
Aaron Ramsey - Juventus to Nice (free). AFP -
Orel Mangala - Stuttgart to Nottingham Forest (£12.7m). AFP -
David Raum - Hoffenheim to RB Leipzig (£21.8m). Getty Images -
Oscar Mingueza - Barcelona to Celta Vigo (£2.5m). Getty Images -
Jules Kounde - Sevilla to Barcelona (£45m). AFP -
Dwight McNeil - Burnley to Everton (£20m). Getty Images -
Arnaud Kalimuendo - PSG to Rennes (£21m). Getty Images -
Filip Kostic - Eintracht Frankfurt to Juventus (£14.4m). EPA -
Salvatore Sirigu - Genoa to Napoli (free). Reuters -
Mikkel Damsgaard - Sampdoria to Brentford (£12.7m). EPA -
Malang Sarr - Chelsea to Monaco (loan). AFP -
Issa Diop - West Ham United to Fulham (£15m). Getty Images -
Alexis Sanchez - Internazionale to Marseille (free). Getty Images -
Timo Werner - Chelsea to RB Leipzig (£18m). AP -
Amadou Onana - Llle to Everton (£33.8m). AFP -
Emirhan Ilkhan - Besiktas to Torino (£3.8m). PA -
Gonçalo Guedes - Valencia to Wolves (£27.5m). AP Photo -
Conor Coady - Wolves to Everton (loan). Getty Images -
Anthony Modeste - Cologne to Borussia Dortmund (£3.8m). EPA -
Angeliño - RB Leipzig to Hoffenheim (loan). Getty Images -
Marcos Senesi - Feyenoord to Bournemouth (£12.6m). AFP -
Isco - Real Madrid to Sevilla (free). EPA -
Raheem Sterling - Manchester City to Chelsea (£50m). Getty Images -
Lisandro Martinez - Ajax to Manchester United (£46m). Getty Images -
Robert Lewandowski - Bayern Munich to Barcelona (£38.3m). AFP -
Hugo Ekitike - Reims to Paris Saint-Germain (loan). AFP -
Thomas Henry - Venezia to Verona (£3.8m). Getty Images -
Takefusa Kubo - Real Madrid to Real Sociedad (£5.2m). Getty Images -
Kalidou Koulibaly - Napoli to Chelsea (£33.8m). EPA -
Chancel Mbemba - Porto to Marseille (free). EPA -
Breel Embolo - Borussa Monchengladbach to Monaco (£10.6m). EPA -
Christian Eriksen - Brentford to Manchester United (free). PA -
Raphinha - Leeds United to Barcelona (£49m). Getty Images -
Federico Bernardeschi - Juventus to Toronto FC (free). Getty Images -
Andrea Cambiaso - Genoa to Juventus (£5.9m). Getty Images -
Arturo Vidal - Inter Milan to Flamengo (free). Getty Images -
Mohamed Bayo - Clermont to Lille (£11.8m). AFP -
Francisco Trincao - Barcelona to Sporting (loan). Getty Images -
Samu Castillejo - AC Milan to Valencia (undisclosed fee). PA -
Lewis Ferguson - Aberdeen to Bologna (£3m). PA -
Keane Lewis-Potter - Hull City to Brentford (£16m). PA -
Alessio Romagnoli - AC Milan to Lazio (free). Getty Images -
Nathan Collins - Burnley to Wolves (£20.5m). PA -
Andriy Yarmolenko - West Ham United to Al Ain (free). AP Photo -
David Ospina - Napoli to Al Nassr (free). Getty Images -
Kristian Thorstvedt - Genk to Sassuolo (£8.4m). Reuters -
Andreas Pereira -Manchester United to Fulham ( £10m). Getty Images -
Gabriel Jesus - Manchester City to Arsenal (£45m). Getty Images -
Steven Bergwijn - Tottenham Hotspur to Ajax (£26.5m). AP Photo -
Andreas Christensen - Chelsea to Barcelona (free). AFP -
Sébastien Haller - Ajax to Borussia Dortmund (£30.8m). AFP -
Flynn Downes - Swansea City to West Ham United (£12m). PA -
Junior Messias - Crotone to AC Milan (£3.8m). Reuters -
Luis Sinisterra - Feyenoord to Leeds United (£21.3m). AFP -
Brais Méndez - Celta Vigo to Real Sociedad (£12.8m). Getty Images -
Moussa Niakhaté - Mainz to Nottingham Forest (£8.7m). Getty Images -
Romeo Lavia - Manchester City to Southmpton (£12m). AP Photo -
Tyler Adams - RB Leipzig to Leeds United (£20m). AP -
Axel Witsel - Borussia Dortmund to Atletico Madrid (free). EPA -
Maya Yoshida - Sampdoria to Schalke (free). AP Photo -
Tyrell Malacia - Feyenoord to Manchester United (£12.9m). AP Photo -
Zeki Celik - Lille to Roma (£6m). AFP -
Ritsu Doan - PSV Eindhoven to Freiburg (£6.5m). AFP -
Divock Origi - Liverpool to AC Milan (free). AFP -
Rolando Mandragora - Torino to Fiorentina (£7m). EPA -
Joao Palhinha - Sporting to Fulham (£17m). Getty Images -
Franck Kessie - AC Milan to Barcelona (free). Getty Images -
Trezeguet - Aston Villa to Trabzonspor (£3.4m). AFP -
Kalvin Phillips - Leeds United to Manchester City (£45m). Reuters -
Giulian Biancone - Troyes to Nottingham Forest (£5m). AFP -
Giuliano Simeone - Atletico Madrid to Real Zaragoza (loan). EPA -
Raoul Bellanova - Cagliari to Inter Milan (loan). Getty Images -
Richarlison - Everton to Tottenham (£50 million). PA -
Fabio Carvalho - Fulham to Liverpool (£5 million). PA -
James Tarkowski Burnley to Everton (free). Getty Images -
Sime Vrsaljko - Atletico Madrid to Olympiakos (free). AP Photo -
Dean Henderson - Manchester United to Nottingham Forest (loan). PA -
Luuk de Jong - Sevilla to PSV Eindhoven (£3.4m). AP Photo -
Henrikh Mkhitaryan - Roma to Inter Milan (free). Reuters -
Cenk Tosun - Everton to Besiktas (free). Reuters -
Andre Onana - Ajax to Inter Milan (free). Getty -
Moussa Sissoko - Watford to Nantes (£2m). AFP -
Corentin Tolisso - Bayern Munich to Lyon (free). AFP -
Vitinha - Porto to Paris Saint-Germain (£34m). AFP -
Romelu Lukaku - Chelsea to Inter Milan (loan). PA -
Lorenzo Insigne - Napoli to Toronto FC (free). AP -
Sven Botman - Lille to Newcastle United (£31.9m). AFP -
Takumi Minamino - Liverpool to Monaco (£15.5m). Getty Images -
Alphonse Areola - Paris Saint-Germain to West Ham United (£7.8m). AFP -
Lucas Leiva - Lazio to Gremo (free). Getty Images -
Joselu - Alaves to Espanyol (free). Getty Images -
Matt Turner - New England Revolution to Arsenal (£4.7m). Reuters -
Fernandinho - Manchester City to Athletico Paranaense (free). PA -
Bartol Franjic - Dinamo Zagreb to Wolfsburg (£6.9m). Getty Images -
Wahbi Khazri - Saint-Etienne to Montpellier (free). AFP -
Tobias Figueiredo - Hull City to Nottingham Forest (free). PA -
Pietro Pellegri - Monaco to Tornio (£3.9m). Getty Images -
Erling Haaland - Borussia Dortmund to Manchester City. Getty Images -
Malcolm Ebiowei - Derby County to Crystal Palace (undisclosed). PA -
Taiwo Awoniyi - Union Berlin to Nottingham Forest (£17m). Getty Images -
Gareth Bale - Real Madrid to Los Angeles FC (free). PA -
Lucas Alario - Bayer Leverkusen to Eintracht Frankfurt (£5.6m). PA -
Sadio Mane - Liverpool to Bayern Munich (£28m). Getty Images -
Armindo Sieb - Bayern Munich to Greuther Fürth (undisclosed fee). Getty Images -
Nick Pope - Burnley to Newcastle (£10m). PA -
Ki-Jana Hoever - Wolves to PSV Eindhoven (loan). PA -
Ryan Fredericks - West Ham United to Bournemouth (free). Getty Images -
Mario Götze - PSV Eindhoven to Eintracht Frankfurt (£3.4m). Getty Images -
Fabio Vieira - Porto to Arsenal (£30m). EPA -
Antonio Rudiger - Chelsea to Real Madrid (free). PA -
Merih Demiral - Juventus to Atalanta (£17.2m). AFP -
Giovanni Simeone - Cagliari to Hellas Verona (£10.3m). AP -
Marc Roca - Bayern Munich to Leeds United (£10m). PA -
Yves Bissouma - Brighton to Tottenham (£25m). PA -
Gavin Bazunu - Manchester City to Southampton (£12m). PA -
Darwin Nunez - Benfica to Liverpool (£64.3m). PA -
Aurelien Tchouameni - Monaco to Real Madrid (£85.3m). AFP -
Nemanja Matic - Manchester United to Roma (free). EPA -
Ryan Gravenberch - Ajax to Bayern Munich (£20m). EPA -
Giorgio Chiellini - Juventus to Los Angeles FC (released). Getty Images -
Cameron Carter-Vickers - Tottenham to Celtic (£6m). AFP -
Alexandre Lacazette - Arsenal to Lyon (free transfer). AFP
