Tom Sykes' disappointing tenure with Yamaha in World Superbikes was brought to a frustrating conclusion in Portugal after he was forced to withdraw following qualifying.

The Briton had been ailing with a shoulder injury all weekend, the legacy of his two accidents last time out at Magny-Cours, causing him to miss out on a position in Superpole.

Indeed, x-rays would later reveal Sykes had a potential crack in the bone that would render him unable to tackle two race distances without considerable discomfort.

A bitter end to a season in which Sykes showed consistency, but was unable to reach the podium at any stage, he was disappointed to exit the title-winning team on such a low note.

"We came here this weekend aware of the injury but still looking to give it everything and end the season on a high," Sykes, who finishes the season ninth in the standings, said. "Unfortunately further x-rays yesterday at the Clinica Mobile revealed a potential crack in the bone which riding is aggravating further.

"I'm not able to ride to my best ability so unfortunately for my health needed to sit out the last two races. I'm very disappointed for the team as I wanted to repay them for the hard work they have put in for me all year."

Once back to full fitness, Sykes will next be seen in Kawasaki colours after announcing a deal with the Paul Bird Motorsport prepared team in the run up to the final round. He will join MotoGP refugee Chris Vermeulen.