Mikel Arteta confronted 16-year-old Max Dowman after Arsenal's teenage star was sent off as the Premier League leaders suffered one of the biggest shocks in League Cup history against fourth-tier Fleetwood Town on Tuesday.
Dowman saw red four minutes from time after an altercation with Fleetwood's Harrison Neal, leaving Arsenal with 10 men and their hopes of avoiding an embarrassing exit hanging by a thread.
Fleetwood then completed the upset, beating Arsenal 5-3 on penalties after a 1-1 draw to reach the quarter-finals, sparking wild scenes at the home of a side currently 18th in England's League Two.
Arteta confronted Dowman as the teenager walked towards the tunnel, delivering a furious, arms-crossed lecture to the academy graduate as Fleetwood's players celebrated on the pitch.
The remarkable result capped a night of drama, with Fleetwood recovering from Arsenal's second-half equaliser to force the tie into a shoot-out.
Goalkeeper Ryan Lynch saved from Bruno Guimaraes before Conor Haughey sent Arsenal goalkeeper Illan Meslier the wrong way with the decisive penalty to send Fleetwood into the quarter-finals.
The visitors had taken a surprise lead in the 21st minute when Aaron Loupalo-Bi shrugged off Arsenal defender Marli Salmon before firing a tight-angle effort beyond Meslier.
The match had already been disrupted early on when play was stopped for more than eight minutes after a drone was spotted flying above the stadium.
Arsenal responded after the interval and levelled four minutes into the second half.
Ceadach O'Neill, making his senior debut, controlled a long ball from Piero Hincapie before delivering into the area, where Viktor Gyokeres converted from close range.
But Arsenal's hopes of avoiding an embarrassing exit suffered another blow four minutes from time when Dowman was shown a straight red card following an altercation with Fleetwood's Neal near halfway.
It was the second red card this month for the teenager, who was also dismissed while playing for England Under-19s during the last international break.
Arteta later defended his reaction, saying he had specifically warned Dowman about keeping his composure.
"When we prepared the context of the match, we were very clear on the things to respect, the things that emotionally we have to dominate. It was very clear," Arteta said.
The Arsenal boss was reluctant to pass judgement on the incident itself, adding: "It's difficult to see on the cameras, so I prefer to watch it back properly and then I can assess the situation."
Asked whether Dowman would learn from the experience, Arteta replied, "Yes, we all learn from everything."
Arsenal pressed for a winner despite being reduced to 10 men, but Lynch produced a crucial late save to deny Ben White and force the tie into a shoot-out.
Lynch then dived low to his left to palm away Guimaraes' penalty as Fleetwood went 4-3 ahead before Haughey completed the stunning victory.
"Amazing for the club, the town. Honestly it means everything to everyone," Lynch told Sky Sports.
Fleetwood had drawn inspiration from Grimsby Town's famous cup victory over Manchester United last season.
"We took heart from Grimsby beating Man United last year. We kind of compared it," Lynch said. "The whole team throughout the game was magnificent. To beat the English champions – credit to these lads."
Arsenal have won seven of their opening eight Premier League matches and are unbeaten in the Uefa Champions League. Fleetwood, by contrast, have won just once in their previous eight league games.
