The Washington Redskins will be without starting Mo linebacker Perry Riley Jr. for the next three to six weeks, as Redskins head coach Jay Gruden announced on Friday he's having surgery.

It's a tough blow for both the Redskins and Perry Riley Jr. – who was having one of the best stretches of his career recently – as head coach Jay Gruden announced on Thursday that the linebacker will be out three to six weeks to undergo surgery following a foot injury suffered during Wednesday's practice.

"He was playing well, very well," Gruden said, "The last two weeks he's been outstanding for us and playing with a lot of confidence. It's a big loss."

Riley Jr. said on Wednesday afternoon that a "turf monster got me a little bit."

The LSU product has started nine games this season, recording 43 tackles with three passes defensed and two interceptions

Those two interceptions came in the last three weeks, as Riley Jr. stepped up following questions about his abilities in pass coverage following a difficult outing against the New England Patriots.

"It's the NFL. We play week to week. I can't bring something that happened last week into this week," Riley Jr. said following his impressive interception off of New Orleans Saints quarterback Drew Brees. "I just have to clear out my mind. I still have a lot of confidence in my ability. I just go out there and play football. Sometimes I'm going to make plays sometimes they might make plays on me. I have to keep fighting and keep my confidence high and keep my mind in the right place and everything else will handle itself."

The Redskins will now more than likely rely on Mason Foster in the starting Mo linebacker role.

While the team could move Will Compton to Mo from Mike, Keenan Robinson, now the team's No. 2 Mike linebacker on the unofficial depth chart, remains limited in practice this week as he continues to work his way back from a nagging shoulder injury that's kept him out of the last three games.

Foster was signed by the Redskins prior to their Week 4 matchup with the Philadelphia Eagles, a game they would win 23-20.

While the University of Washington product hasn't started for the Redskins in his eight games this season, he has started 54 games over the course of his four-year stint with the Tampa Bay Buccaneers from 2011-14.

Foster has 348 career tackles with 12 passes defensed, six sacks, five interceptions, two touchdowns and two fumbles forced.

"He's a pro," Redskins defensive coordinator Joe Barry said. "I think that's the thing I've been most impressed with him during the five, six, seven (weeks), however long he's been here. He came in and went right to work. We've kind of taken every guy, whether it's guys that have been here from the start or guys that we've signed, the first thing I tell them is, 'Don't look at yourself as a backup, you're a starter in waiting.' And I think every single guy in our room knows you're always one snap away from being a starter. He's kind of taken that approach and he's worked his butt off."

Foster describes himself as a "high-motor" player with "really good instincts."

"I always felt like I was a natural linebacker since I was 4, 5 years old," he said in October. "I just really love football, that's the biggest thing. I'm real passionate about the game and I love to play football. I'm a team player, so you're going to see me with a lot of enthusiasm and a lot of passion out there, flying around, that's what I try to do, sideline to sideline."

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