SINGAPORE - Formula One cars are allowed one penalty-free engine switch per season and McLaren's Heikki Kovalainen opted for his Saturday ahead of qualifying for the Singapore Grand Prix.

Mercedes motorsport boss Norbert Haug said they had noticed some wear and tear and with four races left this year decided to make the change.

"We have changed the engine in Heikki's car as a precaution," Haug told reporters.

"We saw a little bit of usage in the engine and this is a 'joker' engine, so there is no grid penalty applied. It is a critical time of the year and if you have it available you should use it.

"We have had very good reliability so far. If you see only a risk of one or two percent, maybe it is even less, then you should use it if you can."

Kovalainen's world championship leading teammate Lewis Hamilton has yet to make use of his backup engine.

A second engine switch in a season results in a 10-place grid penalty.