Barcelona, who dropped out of the Champions League, now face a difficult task of qualifying for the round of 16 in the Europa League.
Making their first appearance in the second-tier European competition in nearly two decades, the Catalans were held 1-1 by Napoli at Camp Nou on Thursday in the first leg of one of eight play-offs between third-place finishers in the Champions League groups and Europa League group runners-ups.
It was the first time since 2003-04 that Barcelona are not in the knockout stages of the Champions League, a tournament they have won five times.
Barca dominated proceedings but found themselves a goal down to the Italians after Piotr Zielinski finished off a counter-attack in the 29th minute.
Barca forward Ferran Torres equalised before the hour mark from the penalty spot after VAR spotted a Juan Jesus handball from a Adama Traore cross inside the area.
Barca were on the front foot throughout with their new attacking trio of new signings Torres, Traore and Pierre-Emerick Aubameyang, but missed several chances to take the lead.
Napoli held on despite a late onslaught in the final ten minutes, with Torres and substitutes Luuk de Jong and Ousmane Dembele missing chance after chance in front of Alex Meret's goal.
"I'm sad because it makes me angry that [Barcelona] missed so many chances because it's a game to, at least win," Xavi said.
"I think that the only thing that we lacked was to convert the chances. We were good in the high press. After going behind, we generated 20 chances and six or seven were very clear.
"It was a complete game. The result should be a victory and, being fair, by at least a couple of goals. We played well, but we're competing in the Europa League. This isn't about feelings, it's about results, and the game was excellent."
Barcelona travel to Italy for the second leg on February 24.
