Defending drivers' world champion Sebastian Vettel crashed heavily in his Red Bull just half an hour into Friday's opening practice session for Sunday's Canadian Grand Prix.
He smashed his car into a wall at about 100kph after running over a kerb at the final chicane at the Circuit Gilles Villeneuve.
The accident caused the marshals to red-flag the session and bring it to a halt.
German Vettel, 23, is the leader of the current drivers' title race, with 143 points ahead of Briton Lewis Hamilton of McLaren on 85.
Brazilian Felipe Massa of Ferrari was the fastest man on the track at the time of Vettel's accident.
He clocked a best time of one minute and 17.431 seconds to lead ahead of German Nico Rosberg of Mercedes and Australian Mark Webber in the second Red Bull.
The session was re-started after five minutes during which the debris from Vettel's accident was cleared.
Red Bull have never won a Canadian Grand Prix in Montreal.