Ben Spies will not participate in tomorrow's Malaysian Grand Prix, Yamaha has confirmed.
Spies went into the weekend hampered by bruising following a crash at Phillip Island, in which he suffered a concussion and tearing of the soft tissue around the rib area.
He crashed again in qualifying in Malaysia, compounding his injuries and ending the session 16th of the 17th riders.
Although Spies insisted he was determined to race in a bid to hold on to fifth in the championship, team manager Massimo Meregalli opened the door to Spies withdrawing, saying: "We have to consider what is best for him."
Following consultation between the Yamaha management and Spies it was jointly decided that he should not compete in order to avoid further risk of injury. He will also miss Monday's 1000cc test in Sepang.
Spies withdrawal leaves the works Yamaha squad with just Katsuyuki Nakasuga, with 2010 world champion Jorge Lorenzo forced out of the weekend with an injury sustained in the warm-up for the Australian Grand Prix.