Van Persie hit a spectacular double in victory at the Liberty.
Michu said: "He had two chances and he scored two goals but that is why Manchester United are fighting for the championship.
"For me, to be honest, he is the best striker in the world.
"He had no clear chances in this game and it is just incredible how he ended up with two goals. It stops with him, he is the best.
"I don't know how many goals he will score this season. A hundred, maybe a thousand! One thing is for sure, he is going to score a lot."
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