MotoGP champion Casey Stoner says he has recovered only 50 percent from injury but is ready to take "life-changing" risks in his comeback to crown his final year in Grand Prix racing. The Australian is set to race at the Grand Prix of Japan on Sunday, having missed the last three events after injuring his right knee in a crash in 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 Honda's Dani Pedrosa, in second place on 257. Stoner is sitting in third position with 186 points with four races remaining. The winner of each race earns 25 points. "Fifty percent, maybe," said Stoner, still seen limping, about the progress of his recovery. "I expected my body to be up around 80 percent, trying to be 70 or 80. 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." 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. "To be honest, I expected more (progress) but the doctors didn't. The doctors warned me that it's going to be six to eight months before we know it's acceptable," said the 2007 and 2011 world champion who turns 27 next Tuesday. "It's only two months so I'm a little bit greedy." 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. Asked if he had thought about the health risks involved, he said: "If I crash again and injure the same foot, then the injury could be, you know, life-changing, for a while anyway. "Honestly, probably, I shouldn't be back here," Stoner admitted. "But I was not going to miss Phillip Island in my last season. For me to at least get back the speed before I get there is better." Three races will be fought over three weeks in Japan, Malaysia and Australia before the season finale at Valencia, Spain, on November 11. Stoner admitted his injured foot still needed to be extensively treated with all his ligaments stretched or torn. He said it was still difficult to make sideways motions with his right foot, adding: "If we get any movement back, we get less stability." Stoner said it was in his nature to race to win. While Lorenzo has won four races in total, Pedrosa was victorious in three of the last four events. Stoner won the other four before he was injured. text he