Factory Yamaha's Ben Spies has been forced to withdraw from tomorrow's MotoGP penulimate round at Sepang and the subsequent test on Monday as the injuries he sustained at Phillip Island have been aggravated by two further crashes.

The former World Superbike Champion had intended to ride through the pain from his 16th place on the grid but after consulting with medical staff and his team, the Texan has called it a weekend. Spies sustained a concussion and tearing of the soft tissue around the rib area after crashing during qualifying for the Grand Prix of Australia, preventing participation in the race.

"Despite starting this weekend with the full intention of racing, two further crashes during today’s practice sessions have highlighted the restrictions his injuries have imposed on his riding abilities," said a team spokesman.

"Following consultation between Yamaha management and the rider it has been jointly decided that it would be wise to not participate in the race to avoid the risk of further injury. He will also miss Monday’s 1000cc test in Sepang. This decision will allow Ben the optimum chance of recovery before the important final race of the season and subsequent 1000cc test at Valencia in two weeks' time."