Ralf Schumacher's Williams caught fire in the Monza pitlane on Tuesday after Formula One teams resumed testing after a six-week ban.
A team spokeswoman said marshals quickly extinguished the flames after an apparent oil leak when the German came in after his first few laps.
"It was nothing major, it looked worse than it was," she said.
Ralf's older brother Michael, the world champion who had a refuelling flare-up at this year's Austrian Grand Prix, was also testing for Ferrari at a circuit that could be crucial to his title hopes when it hosts the Italian Grand Prix next week.
Ferrari, portrayed as a team in crisis by the Italian media after Schumacher was lapped and finished eighth in the last Hungarian Grand Prix, are throwing everything at the tests to regain the title initiative.
Williams lead Ferrari in the constructors' standings by eight points with three races to go while Schumacher's bid for a record sixth drivers' crown looks increasingly shaky with two points dividing the top three.
Colombian Juan Pablo Montoya, first on track in his Williams on Tuesday, is one point behind Schumacher while McLaren's young Finn Kimi Raikkonen is a point further back. Ralf Schumacher is fourth on 58 points, 14 off the lead.
All 10 teams will be testing at Monza this week, with Hungarian Zsolt Baumgartner standing in for injured Briton Ralph Firman at Jordan.
