Defending MotoGP world champion Casey Stoner has flatly rejected speculation he will race V8 Supercars next year.

Stoner, who will retire at the end of the season, will be just 27 when he makes his final appearance at home in the Australian Grand Prix at Phillip Island in October.

Casey Stoner. Credit:Getty Images

He cited a loss of passion for racing and a desire for family time with wife Adriana and baby daughter Alessandra as the main reasons for his retirement.

"Am I going to race V8s next year? No, I'm going to stay home and watch my little girl grow up for a while," Stoner said.