SEPANG, Malaysia (Reuters) - Valtteri Bottas is confident his back has fully healed and he will be fit for the Malaysian Grand Prix this weekend after the Finn missed the season-opening race in Australia despite qualifying sixth-fastest in his Williams.

Claiming that the pain felt like "a knife stabbing in his back" on the eve of the race, Bottas heeded the advice of the sport's governing body (FIA) not to compete in Melbourne but was passed fit on Thursday for the second round at Sepang.

"At the end of last week, I could do something without any pain and, during the weekend, I could do some training, swimming and cross-training without any pain," he said.

Bottas added that he had been working with Williams mechanics to adjust his seat and pedal positions in the cockpit to lessen the impact on his back as it continues to heal.