MotoGP: Ben Spies announces retirement because of injury
Ben Spies has announced his retirement from racing after persistent injury problems left the Ducati rider with concerns over his physical ability.
The 29-year-old American managed just two races this season before he crashed out at Indianapolis in August which left him needing shoulder surgery.
Ex-World Superbike champion Spies has reached an agreement with Ducati over his contract, which had a year to run.
"The time has come to stop and I do so with great sadness," Spies said.
"I never dreamed that I would reach the level of success that I have over the past 20 years of racing.
"But I am tremendously disappointed that I have not been able to fulfil my personal goals and team goals with Ducati."
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 chest pains at a race in Texas in May and missed a string of races after that before the latest setback at Indianapolis in August.
Ducati MotoGP project director Paolo Ciabatti added: "We really hoped he would fully recover and continue to race for us in the future.
"However, we understand the reasons for his decision and respect them."