Double MotoGP world champion Casey Stoner has announced that he will undergo surgery today (Thursday).

Stoner - who will retire at the end of this season - suffered a spectacular qualifying highside at Indianapolis on August 19, which left him with fractures to his right ankle and severe ligament damage.

Although he rode to fourth in the race, the Australian returned home for surgery on the eve of last weekend's Brno round, having been informed by his doctors that he risked permanent injury.

"Going under the knife today, hope everything goes to plan so I can have a quick recovery. I need to finish my last season off," Stoner wrote on his official Twitter page (@Official_CS27).

Although recovery time won't be clear until after the surgery, most expect Stoner to return in October, for the final four rounds of the season - which include Honda's home Japanese Grand Prix (October 14) and Stoner's home Phillip Island round (October 28).

World Superbike star Jonathan Rea is ready to replace Stoner at September's Misano and Aragon rounds.

Stoner - the most successful MotoGP rider since 2006 - has won four races this year and remains third in the championship.

Yamaha's Jorge Lorenzo is 13-points ahead of Stoner's team-mate Dani Pedrosa at the top of the standings.