Barcelona goalkeeper Marc-Andre ter Stegen apologised to his teammates for making the mistake which he felt cost his side the game against Celta Vigo on Sunday.
In a match riddled with errors, which Celta eventually won 4-3, it was Ter Stegen's second-half blunder which stood out.
Pablo Hernandez read the German goalkeeper's decision to clip a risky pass to left-back Jordi Alba at 3-2, closing him down, blocking the ball and diverting it into the back of the Barca net.
Gerard Pique did add a third goal for Luis Enrique's side, setting up a nervy finale, but Ter Stegen conceded his gaffe ultimately ended Barca's chances of getting anything from their trip to Balaidos.
"The game was difficult, as everyone knew it would be," Ter Stegen told reporters. "In the second half we did what Barcelona have to do, but if I hadn't made the mistake we could have won this game.
"I'm sorry for the team, who fought really hard. For me, it was the pass which seemed the right one, but it's an error I don't want to talk a lot about.
"It shouldn't happen. It's worse for the team; I think we lost because of it.
"It's an error, but it's passed. I can't think all the time about what's happened. I have to continue, keep my head up. We continue on the same path, and so do I."
Centre-back Pique defended Ter Stegen, though, stating his firm belief that his teammate's style of play has more pros than cons for Barca.
"We know Marc's good with his feet and a lot of our moves are started by him," Pique told Movistar. "Everyone makes mistakes, but I know that it won't affect anything in terms of how he plays.
"For the goal, could he have taken less of a risk? Yes. But the way he plays gives us so much and often [those risks] are good for us. He should continue."
Pique added his second goal of the game after Ter Stegen's gaffe, but Celta held on for the three points. It was the second season in a row in which Eduardo Berizzo's men have inflicted defeat on Luis Enrique's side in Vigo, scoring four goals on both occasions.
And while Pique was pleased with the fightback in the second period, he conceded that there's plenty to work on after Barca missed the chance to capitalise on Real Madrid's draw with Eibar earlier in the day.
"In the first half we started well, but the [Celta] goal affected us," Pique added. "Then they've scored two quick goals. In the second half we played better and we didn't have anything to lose.
"It almost came off. It's a lesson. You have to highlight the team's reaction and the pride we've shown, but there are a lot of things to learn."