Spies fell while riding in extremely challenging wet conditions at the Sepang International Circuit. An initial check by the trackside medical centre found no serious injuries however further tests conducted on Monday in Kuala Lumpur have revealed injuries requiring surgery.
The Texan will return to the U.S. on Tuesday to receive treatment for an AC shoulder separation, a cracked rib in the upper chest area and bruising to the lung.
"I'm lost for words. We've had such a tough season with an unbelievable amount of bad luck,” Spies said. “We have always gone out there to give it 100 percent and it was the intention of both myself and my team to continue to do so at Phillip Island.
“I took a really hard knock on Sunday and it's now clear from today's tests that I have some injuries that require immediate attention. I'm sorry for my team and thankful for all the hard work they and Yamaha have put in so far; our current situation is not where we should be.”
Yamaha Factory Racing will not field a replacement rider at Phillip Island due to time constraints.