Valtteri Bottas out of Aussie GP with back injury

Williams' driver Valtteri Bottas has been ruled out of the Australian Grand Prix with a lower back injury less than an hour prior to Sunday's race.

Bottas was declared medically unfit to drive by the FIA after suffering the injury during Saturday's qualifying session.

Bottas was set to start sixth but Williams aren't allowed to replace him once qualifying is finished. His teammate, Felipe Massa, starts third.

The injury means just 17 drivers will compete during the race. Manor Marussia were forced to bow out after failing to get its two drivers onto the track for qualifying.

Bottas had a breakthrough season in 2014 with six podium finishes and a fourth overall finish in the drivers' standings.