Right guard Mike Williams suffered a foot injury in the Redskins' 17-0 loss to the Dallas Cowboys on Sunday night.

Williams has been ruled out of the Redskins' season finale against the San Diego Chargers, head coach Jim Zorn said.

The injury occurred in the first half. He was replaced by Will Montgomery the remainder of the game.

"He tore a muscle in his lower foot that attaches to his big toe," head coach Jim Zorn said. "He will be out."

Zorn said no decision had been made who would start in place of Williams.

Montgomery would seem to be the likely candidate. He started three games at right guard earlier this season.

If the Redskins want to get a closer look at a young lineman, then rookie Edwin Williams could draw the start. Williams made his first NFL start in Week 12 at Philadelphia, but has seen limited action since that game.

Also, the Redskins could put Mike Williams on injured reserve and sign another lineman to take his place on the roster for the Chargers game.

Right guard has been a revolving door for the Redskins this season.

The Redskins opened the season with veteran Randy Thomas at the position, but he suffered a season-ending triceps injury in Week 2. Later in the season, backup Chad Rinehart went down with a fractured fibula.

Montgomery, Rinehart, Mike Williams and Edwin Williams have all started at the position this season.

-- DOUGHTY 'DOUBTFUL'

Reed Doughty has a high ankle sprain, putting his availability for the Redskins' season finale next Sunday against San Diego in question.

"He's going to try to fight to play in this last game, but he'll probably be doubtful," Jim Zorn said. "I just have to wait to see how he responds."

The injury occurred after Doughty had made a diving interception of a Tony Romo pass in the second quarter. He got up and raced 13 yards down the sideline, but he was tackled awkwardly by wide receiver Miles Austin.

Doughty was eventually carted off the field.

If Doughty is unable to play, then Kareem Moore would likely join LaRon Landry as the Redskins' starting safeties vs. San Diego.

-- ON FOURTH DOWN

The Redskins' defense remains the league's best when it comes to fourth downs.

On Sunday night vs. Dallas, they stopped the Cowboys offense on two fourth-down attempts in the third quarter.

This season, the defense has stopped 3-of-16 fourth-down attempts, an 18.7 percent clip that is tops in the league.

The Indianapolis Colts are ranked second with a 31.5 percent clip. They have stopped 6-of-17 fourth-down attempts.