Well, first of all, he hasn't been the best player in Europe in a long ass time, man is 37.
Second, it depends on what you mean. Compared to his prime? Of course, yes. Is he totally finished as a player? Nah, I think he has some mileage left. He was scoring a lot in the beginning of the season, and saved Man U's and Portugal's ass a couple times. But Man U are a disaster collectively. His position as an older guy is being a center forward who's less involved with play making, he depends on the team creating chances for him, and grabbing crosses or rebounds in the area. He's undeniably going through a bad streak of games, but that's not necessarily evidence that he's finished. He' probably still a top 15-20 striker in the world, even past prime.