BRNO, Czech Republic - Defending MotoGP world champion Casey Stoner will miss the Czech Grand Prix on Sunday, August 26, 2012 because of an ankle injury that has all but ended his hopes of retaining his title.Stoner, a two-time world champion, is currently third in the overall standings with 186 points, 39 behind leader Jorge Lorenzo with seven races to go.HURT AT INDIANAPOLISStoner said: "I've lost championships before, so we know what it's like. We're pretty much out of it, even going into this weekend. But now that we're not competing, it's done and dusted. Very frustrating, but life goes on."Stoner has already announced he'll retire after this season."It's definitely disappointing," Stoner said. "It's not what we wanted, especially in my last season."Stoner was hurt during qualifying for the Indianapolis GP, sustaining multiple chip fractures and four torn ligaments in his right ankle following a crash during qualifying.Despite the injury, Stoner was cleared to race and finished fourth.A statement on the official MotoGP website said Thursday that the 26-year-old Stoner arrived in Brno but would later leave for Australia to undergo surgery.Stoner said he decided to withdraw following his doctor's advice.SURGERY SOON"The worst thing to do would be to keep going, to keep riding with it," Stoner said the doctor told him. "And the best thing to do would be to get back and have surgery as soon as possible, so that gives us the quickest recovery rate before the end of the season, and hopefully we can get back."Surgery is planned for early next week. It is not clear when Stoner would return to racing."Hopefully they can get me back on track as soon as possible and at least I'll get a few races before the end of the season," he said.Championship leader Lorenzo said the Czech fans will miss out on not being able to see Stoner race."It's very bad news for the championships that Casey retired from the race," Lorenzo said.