Knee ligaments are a strange injury, I tore mine playing football and played on for twenty minutes, it’s not so much painful as uncomfortable and it locks and restricts movement, can feel like a lesser injury that you can run off until you realise that’s not happening. The strong legs a professional footballer has will mask it to some extent as well, some Rugby players can not even realise they have done any damage for ages as the muscles in their legs are able to compensate for the problems the injury causes (although the twisty, turny nature of football makes it a worse injury for a footballer to suffer in my opinion.
Had an ACL replacement and while it is a big improvement for everyday general life no way would I go back to playing football after. Obviously completely different for a very fit, young pro who will have top rehab, but I still hope it’s minimal damage which at most requires a clear out, he was walking as if he had done something in his knee, hopefully it’s meniscus or cartilage rather than ligament damage, much more straightforward recovery from those.