Manchester United goalkeeper Andre Onana took responsibility for his side's 4-3 Champions League defeat by Bayern Munich on Wednesday after his error for the opening goal handed the German giants the initiative.

United had started brightly at the Allianz Arena but never recovered from the moment Leroy Sane's strike slipped through Onana's grasp on 28 minutes.

The Cameroonian starred for Inter Milan on their run to last season's Champions League final, but has struggled in the early weeks of his United career since joining in a £47 million ($58 million) move.

Bayern Munich's German midfielder #10 Leroy Sane scores the opening goal past Manchester United's Cameroonian goalkeeper #24 Andre Onana during the UEFA Champions League Group A football match FC Bayern Munich v Manchester United in Munich, southern Germany on September 20, 2023. Photo: AFP

The Red Devils have now conceded three or more goals in three consecutive games for the first time since 1978.

"After my mistake we lost control of the game. It's a difficult situation for us, for me especially because I'm the one who let the team down," Onana told TNT Sports.

Serge Gnabry quickly doubled Bayern's advantage.

Rasmus Hojlund's first United goal briefly brought the visitors back into the game, but Harry Kane's penalty restored Bayern's two-goal lead.

Casemiro scored twice in a chaotic finale, either side of Mathys Tel's fourth for Bayern, but United have now lost four of their opening six games of the season.

"My start in Manchester is not so good, it's not how I want (to play)," added Onana.

"Today is one of my worst games and it is difficult because we have big ambition, we want to win everything, it was a big opportunity for us to bounce back after the situation we are facing.

"It's a tough time. We have to be together and learn from our mistakes because it's the only thing to do."