Redskins head coach Mike Shanahan said that Thomas will undergo surgery and is expected to be out four to five months. Thomas will be placed on the season-ending injured reserve list.
Thomas was a fourth-round selection in April's draft and started the Redskins' preseason opener August 8 against the Tennessee Titans.
“You lose a guy [and] competition still goes on,” Shanahan said. “These guys are one play away from being the starter. We’ve got a lot of quality players out there.”