American MotoGP rider Ben Spies announced his retirement from racing on Saturday after being sidelined by injury and starting just two races this season.
The 29-year-old Tennessee-born former world superbike champion and Italian manufacturer Ducati said in a statement that both parties had agreed to terminate a contract that still had a year to run.
"I never dreamed that I would reach the level of success that I have over the past 20 years of racing, but the time has come to stop and I do so with great sadness," Spies said.
Spies injured his right shoulder a year ago in Malaysia while racing for Yamaha, missing the last two races of 2012 and the start of pre-season testing for the factory-supported Pramac Ducati team.
He suffered muscle pain at the race in Texas in May and missed a string of races after that. He then suffered a further setback when he crashed in free practice at Indianapolis in August. He has had operations on both shoulders.
"We really hoped that he would fully recover from his Indianapolis crash injuries and continue to race for us in the future. However, we understand the reasons for his decision and respect them," Ducati MotoGP project director Paolo Ciabatti said.