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08/14/12 3:03 AM ET

Sore ankle scratches Werth from Nats' lineup

SAN FRANCISCO -- Jayson Werth sat out of Monday's series opener against the Giants at AT&T Park due to a sore right ankle, and he will undergo a "precautionary" MRI on Tuesday morning.

The Nationals announced about 45 minutes before the game that Werth, who was slated to bat sixth and play right field, wouldn't start. He wore a boot on his right foot Monday night and said he "definitely" couldn't have played, although he added, "I don't think it's serious."

Nationals manager Davey Johnson said he first noticed the injury Sunday, when Werth pinch-hit, ran to first and limped a bit afterward. Werth has dealt with similar injuries before, and he hoped to be able to play Tuesday night against the Giants, although, he joked after the Nats' 14-2 romp, "They don't need me anyway."

Werth has been dealing with general soreness, particularly in his legs, since returning from the disabled list Aug. 2. The outfielder left a game in Houston on Aug. 6 due to leg soreness, but he was back in the starting lineup Wednesday after Johnson kept him out of the starting lineup for precautionary reasons last Tuesday.

The Nationals are 9-0 in games Werth has started since coming back from the disabled list. In his place Monday, Michael Morse moved from left to right field, shortstop Danny Espinosa was bumped up from seventh to sixth and Roger Bernadina was slotted into the lineup, batting seventh and manning left field.

"Hopefully it's something that in a day or so, he's fine. I didn't want to play him," Johnson said. "Hopefully he'll be OK to go [Tuesday]."

Morse, meanwhile, jammed his right thumb during batting practice and was replaced by Tyler Moore in the fifth inning. Morse said afterward he felt fine and expected to be back in the lineup Tuesday.

Desmond's rehab keeps chugging along

SAN FRANCISCO -- Ian Desmond is ramping up his rehab once again.

Desmond, on the disabled list since July 22 with a torn left oblique, went through his first full pregame workout with the Nationals on Monday at AT&T Park. Desmond was scheduled to take batting practice, field ground balls and participate as if he were going to play in Washington's series opener against San Francisco.

The shortstop has been speeding through rehab milestones over the last week or so. He began taking grounders in Houston last week, started hitting in the cage this weekend in Arizona and now, he's going through a full workout on the field.

"Hopefully he comes through that with no problems," Nationals manager Davey Johnson said. "He's had no tenderness in that area. That's great. So if he continues to go through his workout, no need to speed it up."

Desmond is scheduled to participate in two more full pregame workouts with the Nationals in San Francisco, then the club will make a decision after that. Johnson said there is a plan in place for Desmond, "and I'm not telling you. I want him to get through these three days.

"I've got a little plan in the back of my head," he added. "If we get through Wednesday, I'll tell you what it is. You'll know by then."

However, Johnson didn't seem to be in favor of Desmond going out on a long Minor League rehab assignment. Many players will say they need those games in the Minors just to get back their timing and see if they can withstand the rigors of a full nine-inning game. But Johnson, who previously has said he wants Desmond back as soon as he's fully recovered, doesn't think Desmond will need too long.

"Timing is going to be different for every pitcher you face. As long as you're healthy and your stroke is fine -- which his stroke is outstanding -- you catch up pretty quick," Johnson said. "I don't think it's going to help his timing [against] guys in [Class A] Potomac, who throw it 100 and don't throw it over."

Nationals could adjust rotation after off-day

SAN FRANCISCO -- Entering Monday, the Nationals were three games away from an off-day. That might not seem like a big deal, but it will also mark the end of a stretch during which they played 35 games in 34 days.

Along with a much-needed chance to rest, it will give Washington manager Davey Johnson an opportunity to tweak his starting rotation. He wasn't ready Monday to announce exactly how he would do so, but he said he has been thinking about it.

"I'm not going to do anything the next three days, and that's all I'm concerned about," Johnson said. "This time of year, you go further out about how you want the pitching to line up coming down."

Right now, the Nats' two left-handers, Ross Detwiler and Gio Gonzalez, are lined up to pitch on consecutive days. By shuffling it, Johnson could break up the lefties and give right-hander Jordan Zimmermann, still dealing with some right shoulder soreness, an extra day to rest between starts.

Johnson said he would like to switch up the order of his rotation because it allows him to better organize his bullpen, specifically his long relievers. He can also start one of his pitchers against a team he's had a particularly high level of success against.

But there's another factor in play as well: In a pennant race, Johnson can line up his starters for a certain series -- like, for example, next week's three-game showdown with the Braves at Nationals Park.

"That's right," Johnson said. "That would be one of the reasons."

Adam Berry is a reporter for MLB.com. Follow him on Twitter at @adamdberry. This story was not subject to the approval of Major League Baseball or its clubs.