When people say Onana is not performing well, I remind them that they entire team is underperforming. How do you expect a goalkeeper to be outstanding when the defense is weak. The confidence of a goalie is a good defense. Maybe a top team might not want him due to his lack of confidence and numerous costly blunders. But I am sure that an average or low-placed club can buy him. He would have to reduce his earnings and maybe sign a short term contract.
Espanyol's goalkeeper prove it.
Joan Garcia played in mediocre team with mediocre players and never played for Spain's senior team, but he has the highest ratings among his teammates. That's show no matter how bad the teammates you have, if you're good, then you good.
Onana in this season is top 10 players, not a great achievement, but not that bad too.