US MotoGP rider Ben Spies has announced his retirement, saying injuries to both shoulders had hindered his physical ability to ride.

“I want to thank everyone from racing organisations, factories, teams and all my fans for helping me and supporting me throughout my career,” said Spies, who had inked a two-year deal with Ducati to race with the factory-supported Pramac team in 2013 and 2014.

“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.”

The 29-year-old Texan had injured his right shoulder riding for Yamaha in the 2012 Malaysian Grand Prix.

The rehabilitation of that injury dragged on, and he suffered a further setback when he crashed in practice at Indianapolis this year and dislocated his left collarbone.

Ducati said that they had released Spies from any requirement to race in 2014.

Paolo Ciabatti, Ducati MotoGP Project Director, said the company regretted it would not be working with Spies.

“It is really a shame for our sport that Ben will not be racing anymore because in our opinion he is one of the most talented riders in the world,” Ciabatti said.