The Red Devils’ Champions League aspirations were dashed on Wednesday when they were held to a 3-3 draw by the Turkish heavyweights.
Erik ten Hag’s team appeared to be on their way to triumph after Alejandro Garnacho and Bruno Fernandes put them up 2-0 inside 20 minutes.
However, Hakim Ziyech’s free-kick around the half-hour mark appeared to catch Onana off guard, making for a tense half-time finish.
Scott McTominay restored United’s two-goal lead shortly after the break, but Onana was again at fault from another Ziyech free-kick, allowing the ball to tumble between his gloves and into the back of the net.
Kerem Akturkoglu then completed the comeback 10 minutes later, leaving United hoping for a miracle on matchday six to go to the knockout stages.
Since then, footage has emerged showing Onana appearing upset at full-time, slamming his gloves to the field in disgust before burying his face in his hands.
Manager Erik ten Hag, on the other hand, refused to criticize his goalkeeper, saying after the game: “We win and lose together. He [Onana] is okay. It is not about individuals.
“Individual errors in football can make a difference and you take responsibility for it, but it is always about the team.
“All the players in this squad deserve to play for Manchester United because they are brilliant players.
“We are very happy with our keeper group. They do very well and have good performances. They have to push each other.”