However, Sampras has warned the Canadian 22-year-old, who takes on countryman Vasek Pospisil in the semi-finals of the Montreal Masters this evening, that success will not happen overnight.
"He's up against [Novak] Djokovic and [Andy] Murray and Roger [Federer] and four great players, and it takes time," Sampras told reporters. "I think he's a threat already. I think he's got a huge game, monster serve, willing to come in and do some things and get to the net.
"I didn't figure this game out until I was probably 22 or 23, so when everything was settled in I was physically and mentally great. I knew where I stood in the game. It just takes time.
"I know Milos does the right things; he works hard; he wants to do well. He just has to be patient. It isn't going to happen overnight."