MotoGP champion Casey Stoner says he has recovered only 50 per cent from injury but is ready to take “life-changing” risks in his comeback to crown his final year in racing.

The Australian is set to race at the Grand Prix of Japan tomorrow, having missed the last three events after injuring his ankle in a crash while qualifying at the Indianapolis Grand Prix in August.

The Honda rider’s absence means it is now impossible for him to retain his crown, with the 2012 championship currently led by Yamaha ace Jorge Lorenzo, on 290 points, and Stoner’s team-mate Dani Pedrosa, in second place on 257.

Stoner is sitting in third position, on 186 points, with four races remaining. The winner of each race earns 25 points.

In yesterday’s free practice, he needed the help of pain-killers as he clocked the seventh best time while Pedrosa topped the timesheets.

“I just needed ordinary pain-killers to take the edge off,” he said.

“I don’t really like using pain-killers because it wears you off especially when your body’s circulating everything so quickly.”

About the progress of his recovery, Stoner said ahead of the practice: “Fifty per cent, maybe.”

“I expected my body to be up around 80 per cent. But it’s not even close to that right now. So I’m a little bit disappointed that we didn’t make a little more progress with the injury,” he said.

Stoner underwent surgery on August 30 after suffering torn ligaments and fractures to his ankle, tibia and fibula at Indianapolis, although he still lined up for the race and finished fourth.

He had intended to make his return to racing at his home Grand Prix at Phillip Island on October 28, but instead opted for an early comeback at Honda’s home track.