"I think the torn ligaments are really the problem," Seahawks coach Pete Carroll said. "I don't think he's going to have to have an operation, from what I understand."
With 5 minutes, 36 seconds remaining in the first quarter, Rawls lost 3 yards on an inside run and was tackled by defensive lineman Chris Canty. The medical staff tended to Rawls on the field, and he eventually walked to the sideline under his own power.
Rawls had a big impact as a rookie, rushing 147 times for 830 yards. Now the Seahawks have to figure out their options going forward.
One possibility could be the return of Marshawn Lynch, who has missed the past four games as he recovers from surgery associated with a sports hernia injury.
"We'll see how Marshawn does," Carroll said. "He was back in rehabbing with us. We'll see where he is. He's got a chance to get back.
"It's all about getting back in shape and getting right. I don't know what that timetable is at this point. Our trainers can't tell yet. That'll be the next thing we look forward to and see how that works. And in the meantime, we'll figure it out."
DuJuan Harris carried 18 times for 42 yards Sunday after Rawls went out.
Seahawks star safety Kam Chancellor also left the game in the first quarter with a bruised tailbone. Carroll said he has a chance to be back by the end of the week.