The two-time MotoGP world champion says he has grown tired of the discipline after five years competing in the elite division , and will bow out at the end of this season -- which still has 15 of the 18 races remaining . Seven -time MotoGP world champion Casey Stoner to retire at the end of this season . The Australian says he no longer enjoys the motorsport as much as he did . The Honda rider tops practice ahead of Sunday 's Le Mans Grand Prix in MotoGP . Two -time title winner Valentino Rossi aims to stay in the sport for the end of this season .
Seven -time MotoGP world champion Casey Stoner to retire at the end of this season . The Australian says he no longer enjoys the motorsport as much as he did . The Honda rider tops practice ahead of Sunday 's Le Mans Grand Prix in MotoGP . Two -time title winner Valentino Rossi aims to stay in the sport for the end of this season .