Silvestre is training with United as he seeks to extend his career.
"He's very hard to defend against in training," Silvestre told manutd.com about Van Persie. "It's really tough to get the ball off him. He's a top quality player. The arrival of Robin and Shinji [Kagawa] has been great - they have both been fantastic additions to the squad.
"Robin in particular has been amazing since he joined. He came with a lot of pressure on his shoulders but he's responded as well as he possibly could have. He's been brilliant."