You can see hes a very good player, thats plain to see, but when he goes missing for large portions of the games and jogs around the pitch watching the game being played in front of him, well, his potential or his best doesnt help us.
This Newcastle goal explains it perfectly.
Godfrey heads the ball in midfield, Onana makes no attempt to even win the 2nd header, he then watches as Newcastle attack and score whilst casually jogging back.
So yeah, litmus test for sure.
You do see that Onana is doing absolutely what he should be here right? If he goes for that ball, that he’s nowhere near btw (You can also level that criticism at Godfrey who is an equal distance away but that would be equally braindead and neglecting his defensive duties!) and is also falling directly onto Ganas head (I’ve put a green circle round him in case your S tier monitor didn’t pick it up ) then he should be rightly criticised for leaving the middle of the pitch unguarded and that he had zero positional awareness. I’m all for criticism of underperforming players but that is crazy.