"If I ever am up against a rival driver who blows me off the course," the Ferrari driver told Die Welt newspaper on Wednesday when asked when he would retire.
"Then it would probably be better to quit than to do everything to fight that and end up risking my life."
Schumacher, 34, has a record 68 career wins and will be starting his 188th race on Sunday at the European Grand Prix at the Nuerburgring, not far from his hometown of Kerpen.
The German, who has won four of the last five races, leads the championship by three points from McLaren's Kimi Raikkonen.
"If I hit my limit and notice that 'hey, here is someone better who hasn't reached his limit', then it would probably be time to say that's the end of it," said Schumacher, who recently extended his contract with Ferrari by two years to 2006.
Schumacher said he believed being in top physical condition was an important and underrated part of his success.
"I have always worked out hard," he said. "My philosophy has always been to be physically more fit than the others because I believe that ultimately leads to having a mental advantage over the competition."
Schumacher said there were some parts of the changes made this season aimed at making Formula One more attractive for fans that he liked and others he didn't like -- for instance the new point system that awards points to the top eight drivers.
"Isn't it a bit strange that I have won three races and Kimi Raikkonen has won just once, and yet I have just a three-point lead in the standings," Schumacher said.
