It didn't look that bad, but knee injuries can be deceptive. I once stepped wrong and felt this sharp nerve pain in my knee. I could walk on it and put weight on it, but slight changes of angle were a huge problem. Something like playing hockey would be impossible, even though you can walk. It took me almost 4 months for the knee to return to somewhat normal.
Point is, the knee is delicate and any injury is especially felt in a sport like hockey, that requires putting pressure on the knee from the sides. So you can't just look at whether he was able to put weight on it or screamed in pain. It might still not be fine for hockey.
It is a shame, too, since Ovechkin was actually leading NHL in goal-scoring and seemed to have a serious resurgence this year. It would have been cool to see what he could still do at his age, but now it's quite likely that his form will be gone whenever he does return to playing. We'll see, though.