Michael Schumacher may quit Formula One before his Ferrari contract expires in 2006 if he stops winning, Colombian Juan Pablo Montoya said on Thursday.

Montoya, talked of in the Italian media as a likely replacement for the five times world champion when he decides to retire, saw little significance in the 34-year-old German's decision to extend his contract until 2006.

"If he's not winning, he'll probably retire before (2006)," the Williams driver told a news conference ahead of Sunday's Canadian Grand Prix.

"At the moment for him to make a decision and stay winning is not as difficult as if suddenly Ferrari starts to struggle. I think everything could change.

"I don't know Michael, so I don't know, but I'd be surprised if he's not winning if he stays more years, it wouldn't look that good," said Montoya.

Schumacher has won three races this year but remains four points behind McLaren's Kimi Raikkonen, who has yet to race the Mercedes-powered team's new car, at the halfway point of the season.

The German has rewritten most of the sport's records, winning an unprecedented 67 races and now seeking to become the first driver to win six championships.