Ahead of Saturday's Champions League final between the two clubs, Pique is remaining cautious of his former teammate who he spent time with at Old Trafford between 2004 and 2008.
"He is one of the best strikers in the game and has scored a lot of goals," said Pique.
"I will have to concentrate hard to not to give him space. I have a good friendship with him but we both want to win this game and we will be fighting for our own interests.
"It was always difficult playing against him in training as it is with (Lionel) Messi now."
And Pique also heaped praise on United boss Sir Alex Ferguson who he feels had a good influence on his career.
"He has won loads of titles and although the teams change he keeps on winning. I had several really good years there but Barcelona is my home and I wanted to return here. He (Ferguson) understood this," added Pique.