Ben Spies will be forced to miss this weekend's Australian Grand Prix as a result of the injuries sustained in a heavy crash at Sepang.
Though he was initially passed as fit following his high-side in wet conditions at Malaysia, further tests conducted at Kuala Lumpur revealed surgery is needed.
Yamaha confirmed 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 and bruising to the lung. The statement added that "Yamaha Factory Racing will not field a replacement rider at Phillip Island due to time constraints."
Spies first revealed his injury woe on Twitter, ahead of Yamaha's statement. He did likewise when confirming he would leave the team at the end of the season back at Mazda Raceway Laguna Seca.
"It's amazing how I'm suppose to be quiet about my injuries till something formal goes out but when I get back to the hotel everyone knows?," he tweeted.
In the subsequent statement, Spies said he was "lost for words" about the situation, the latest addition to his year of horrors.
"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. It's disappointing to be heading back to the USA now instead of to Phillip Island but it's obviously important to get the right treatment as soon as possible. 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."
It remains unclear whether Spies will return for the Valencia season finale, his last event as a Yamaha rider before joining the Pramac Ducati squad next year. The first 2013 tests will take place immediately after the final weekend.