By John O'Brien
SEPANG, Malaysia (Reuters) - Valtteri Bottas is confident his back has fully healed and he will be fit for the Formula One 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 told reporters.
"We've been doing everything we can in this short space of time but luckily there was two weeks (gap) and I really feel confident about getting back in the car.
"It has healed really well and it's going to keep getting better and better all the time."
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.
"The back is in a more neutral position in the car, so there is less pressure for the discs. Now, I think we have got it right," he said.
"It's quite a big amount of changes to make sure everything is in a neutral position with the back so when the compression comes, it goes to all the discs with similar pressures."
The Mercedes-powered team finished third in the constructors' standings last season and with Red Bull's Renault engine appearing to have regressed over the winter, Ferrari have shown enough improvement in testing and the opening race to suggest they will be Williams' main rivals for second.
Although Sebastian Vettel finished a distant third behind the dominant Mercedes duo of Lewis Hamilton and Nico Rosberg on his Ferrari debut in Melbourne, Bottas' team mate Felipe Massa conceded that fourth place was about the best he could have managed in Australia.
"We don't have an advantage on the straights anymore," Massa said of the Williams. "That's really one thing Ferrari showed they have improved massively. They have a much better system and a much better engine compared to last year.
"Last season, we had less downforce than Ferrari but we gained on the straights. This year our car is much better on the corners compared to last year but we didn't start the season as well as we ended the last one," he added.
"We don't have such an advantage over Ferrari on the straights now so aerodynamics is more of a major factor and we need to work on it as strong as we can as we are fighting with a top team."
(Editing by Sudipto Ganguly)