Double world champion Mika Hakkinen has hinted he could have further tests for McLaren after returning to the cockpit of a Formula One car this week.
Hakkinen said he was surprised how little had changed since 2001
The 38-year-old Finn, champion with McLaren in 1998-99, did a three-day test at Spain's Circuit de Catalunya.
Asked whether he would run again, Hakkinen told Autosport.com: "Naturally, to start doing more tests I will get stronger and quicker.
"But I don't know. We have to discuss and think about and see what happens."
Hakkinen ended up slowest of the 18 drivers at the test, and was more than three seconds adrift of the pace-setter, Ferrari test driver Luca Badoer.
But Hakkinen, who has yet to commit to another season for Mercedes in the German Touring Car Championship, said: "After five years, to come back in F1 and to go very hard, flat out, I think I would make mistakes.
"The risk would be damaging the car. That would first of all not look professional and I don't think I would learn anything then.
The purpose was not to impress anybody enormously, it was just to get a 100% good feeling with the car
"I think it would be unfair for people to automatically expect, after five years, I could go maximum attack and bang in a time."
He said his experience had been useful for the team, who cannot run double world champion Fernando Alonso until the new year because of his contractual commitments to former team Renault.
Alonso's team-mate in 2007 will be novice Lewis Hamilton, who was fourth fastest, 0.7secs slower than Badoer.
"We did manage to make changes, which they hadn't done for a long time," Hakkinen said.
"The purpose was not to impress anybody enormously, it was just to get a 100% good feeling with the car and understand if it has changed a lot since 2001.
"Surprisingly, the changes were very little."