FOXBOROUGH, Mass. -- New England Patriots running back Dion Lewis left Sunday's game against the Washington Redskins after sustaining what appeared to be a serious knee injury with 5:40 remaining in the third quarter.

Lewis is expected to undergo an MRI on Monday. A source told ESPN NFL Insider Adam Schefter that while there is no swelling yet in Lewis' knee, his ACL appears loose.

Lewis was tackled from behind by defensive lineman Chris Baker at the end of a 14-yard catch-and-run and television replays showed him reaching for the area of his left knee as the play was ending.

Lewis, who has been a spark plug for the Patriots with his sharp cuts and knack for stopping and starting in an instant, had remained down on the ground as the medical staff came onto the field. He eventually walked off the field slowly under his own power and headed straight to the locker room for medical tests.

As Lewis walked through the bench area, defensive coordinator Matt Patricia wrapped the dejected Lewis in an embrace.

"It's such a physical game and it's tough to lose such a special player," quarterback Tom Brady said. "I hope he's OK. I don't know exactly what it is but we're all hoping for the best."

Lewis entered the day with 220 yards on 45 carries with two touchdowns, as well as 32 receptions for 349 yards and two touchdowns. He had just four carries for 14 yards in Sunday's 27-10 victory.