Casey Stoner says his chances of retaining his MotoGP title are "finished" after breaking his ankle at Indianapolis last weekend.
Stoner, who will fly back to Australia for surgery and will miss Sunday's Czech Grand Prix, says he has "no idea" when he will return.
"Until we've had the surgery we won't know," said the 26-year-old Australian, who retires at the end of the season.
"It's disappointing news but it's finished our championship."
Stoner currently lies in third place in the standings, 39 points behind leader Jorge Lorenzo with seven races remaining.