The Frenchman was speaking about Martinez during the World Cup, with the Argentine centre-back starring for his country in the group stages so far.
Martinez had been criticized for his lack of height when he first signed for United from Ajax this past summer.
"This is one of the best signings we've had for years at Manchester United," Evra told Vibe with Five.
"It's because of his fighting spirit. That's what United fans want to see – those players have to bleed for the shirt.
"People were talking about his height and I was laughing. Some people said I was too small when I arrived in the Premier League as well. When you play with that heart and passion, size doesn't matter.
"When he gets the ball, he is so clean and composed," added Evra.
"Mexico [during World Cup group stage game] were pressing everywhere but every time he got the ball he was calm and playing forward. That's what I love."