Onana has been criticized for weeks for his performance. Altay Bayindir is a good goalkeeper. Erik ten Hag should give him a chance. Altay Bayindir can perform better than Onana these days.
Galatasaray are becoming a better team day by day. After 3 weeks I have no doubt that we will see a better Galatasaray in the match against Bayern Munich. It's easy to say that already. I wish we had won against Copenhagen, then I would have been braver about our chances of qualifying for the next round.
Altay Bayindir has been known as a promising goalkeeper for a long time. However he started to make simple mistakes at Fenerbahce and this went on for some time until leaving the team. But I don't also believe he is a bad goalkeeper in fact. He must have lost his concentration in the recent times which must have led to that result.
While Onana is making mistakes quite often Altay might be really given a chance by Erik ten Hag soon. They don't have anything to lose about this topic. If not much thing changes then they have nothing to do other than waiting for one of their goalkeepers to improve or signing a new goalkeeper.