"He is the best player in the world and he still could spring to life," Silva told a news conference on Saturday ahead of the first Copa meeting between the sides since the 2007 final, which Brazil won 3-0.
"We will have to be especially focused on him when we have the ball and when we don't. Sometimes he can be at walking pace during a game but he's always looking for space to launch a counterattack.
"It's a privilege to be able to face him again and we'll have to try and put the brakes on him."
Messi has scored once in the tournament -- from the penalty spot -- and has acknowledged he is not playing at his usual level. He had only three shots during his side's 2-0 win over Venezuela in the quarter-finals, none of which hit the target.
"The truth is I'm not having my best Copa America, it's always very difficult for us because we want to do something different and attack and teams pack out the middle of the pitch," he said.
"No one is giving anything away cheaply in this Copa, it's very difficult to play because the pitches are very bad, it's shameful. The ball is like a rabbit, it can go anywhere and you can't dribble."
Argentina winger Angel di Maria says Messi is working hard for the team even if he is not making it onto the scoresheet.
"We are used to seeing him score goals but Leo is doing very well, he is running a lot, he is working hard," he said.
"He knows more than anyone that at this Copa America the first thing you need to do is run, then you can think about the rest, playing well and scoring."
(Reporting by Richard Martin; Editing by Peter Rutherford)
