Knee injuries are some of the most serious injuries a player can have. They're very likely to be career-ending. Most players never get to top form again and some become absolute shit, like our fellow Torres here. Michael Owen, Joe Cole even our brazilian legend Ronaldo never got back to their top form. Ronaldo could still manage to become an awesome striker by changing his style which previously relied on pace heavily. But even him was never as good as before. His goal/game ratio dropped from about 1:1 to 1:2. He had become about half the player he was, and he only managed that because he had clinical finishing, very good positioning and was a marvelous dribbler. Torres is none of those.