DENVER -- Nationals outfielder Elijah Dukes was placed on the 15-day disabled list on Thursday, retroactive to Aug. 3, due to a right calf strain. He is expected to miss four to six weeks.

Dukes hurt the calf on Saturday night in a game against the Reds at Nationals Park. Dukes said that day he hit himself on the calf with his bat on his backswing and started to feel pain.

Dukes declined to talk to the media on Wednesday after it was learned he would be on the DL for the third time this season. Dukes had to be shelved in the past because of right hamstring and knee problems.

While Dukes is expected to miss an extended period of time, Washington manager Manny Acta wouldn't put it past the outfielder returning in less than four weeks. After he hurt his knee on July 5 against the Reds and had surgery to repair a meniscus, Dukes wasn't expected back until late August or early September. However, he returned to action in less than four weeks.

"You can't put a time frame on him because he is a quick healer," Acta said. "It's very tricky, because the calf is a tough injury. Anytime you push off the leg, you put pressure on it. It takes longer than a lot of people think."

With Dukes out, it most likely means Willie Harris will be the Nationals' everyday left fielder. Acta has found a way for Harris to play often at different positions.

During the second half of the season, Harris arguably is the Nationals' MVP, hitting .304 with four home runs and 15 RBIs entering Wednesday's action.

Meanwhile, the Nationals recalled right-hander Garrett Mock from Triple-A Columbus. Mock, who was sent down to the Minor Leagues on Friday, last pitched on Tuesday, giving up a run in 2 1/3 innings against Norfolk. He is expected to be a long reliever for Washington.

Mock was supposed to stay in the Minors for a minimum of 10 days, but he can come back to the Majors before that time if another player is injured. The original plan was for right-hander Tyler Clippard to come to the big leagues in case the Nationals needed an extra man out of the bullpen.

This past Saturday, Clippard started for Columbus, going four innings and giving up two runs against Louisville. He struck out six batters, walked none and threw 50 pitches.

Clippard is 1-1 with a 4.35 ERA in two games with the Nationals this year.