World champion Casey Stoner could be forced to miss Sunday's Czech Grand Prix after breaking his ankle and damaging ligaments in a fall at last weekend's Indianapolis race.
Stoner, who will retire at the end of the season, suffered the injury in a crash during qualifying but still managed to finish fourth in a race won by Honda team mate Dani Pedrosa.
He admitted on Thursday that he was still uncertain over his participation at Brno and would likely make the decision on Friday.
Stoner, who is third in the world championship, 21 points behind second-placed Pedrosa, said: “I'm not feeling too optimistic for Brno after a tough weekend in Indy. The crash in qualifying last week has left me with a serious problem in my ankle.
“In Brno there are many changes in direction and a lot of right hand corners so there will be a lot of weight on my ankle and it's going to be very difficult.
“I'll be resting as much as possible this week and wait to see how we feel when we get on track on Friday,” said Stoner.
World championship leader Jorge Lorenzo was upbeat about his chances in Sunday's race despite pressure from Pedrosa.
“After very little rest we are back in Europe at Brno, a track I really like and where I got a great victory in 2010 on my way to the title,” the Yamaha rider, who finished fourth in Brno last year, said.
“Our tyre choice last year made it difficult to fight for the podium but I think this year with the 1000cc we can definitely fight at the front,” added Lorenzo, who has collected 225 points from 11races so far this season.
Former world champion Lorenzo's lead over Honda rider Pedrosa shrank to 18 points last Sunday, and he will face tough competition from his compatriot on the 5.403km Brno circuit, about 180km southeast of the Czech capital Prague.
Pedrosa crashed out of last year's race, but he said he was hungry now for a second victory on the “wide and very fast track, with high speed corners where it is important to have good grip and front end feeling”.
“Honda has been strong in the past few years, so we hope to have a good performance in this race also.
“The setup of the bike and electronics can be key, as well as the weather, which is always a little changeable in the Czech Republic. We need to keep focused and strong and with options for the victory every weekend,” he said.
The Brno circuit named after Tomas Garrigue Masaryk, the first president of former Czechoslovakia, was opened in 1987 to replace an old circuit nearby that became too dangerous for riders.