CHICAGO -- Nationals third baseman Ryan Zimmerman didn't start in his fifth consecutive game after tweaking his right hamstring against the Rockies this past Wednesday.

Zimmerman said the hamstring is getting better, however the weather is playing a role as to why he is not in the lineup. It's expected to be windy and cold Monday and Tuesday night and the team does not want Zimmerman getting hurt in abnormal conditions.

Manager Jim Riggleman declined to say if Zimmerman is out for the three-game series against Chicago.

"He is making a little progress," Riggleman said about Zimmerman. "Still, he feels [the pain enough] where if he busts out of [the box] really hard, he has a chance to aggravate it. In this cold weather, we are going to be conservative on how we use him. We are going to use him strictly as a pinch-hitter right now."

Zimmerman entered Monday's game as a pinch-hitter in the ninth inning and flied out to deep right field.

Morgan has been running on empty of late

CHICAGO -- Before Monday's game against the Cubs, Nationals center fielder Nyjer Morgan had a talk with manager Jim Riggleman about being caught stealing four times in nine attempts.

Morgan wondered if sliding feet first is the reason he has gotten off to a slow start when it comes to stealing bases. The Nationals want him to slide feet first in order to prevent a hand injury. Last August, Morgan missed the final month of the season after breaking his left hand sliding headfirst into third base against the Cubs at Wrigley Field.

During the talk, according to Morgan, Riggleman gave him the go-ahead to slide headfirst on certain conditions.

"If it's going to be close, go headfirst. If I know I can get it for a fact, go feet first," Morgan said. "I feel comfortable with my hands."

Morgan plans to wear protective guards for his wrist and hands while he is on base.

Harris' knee getting better

CHICAGO -- Willie Harris' ailing right knee was well enough for him to take batting practice before Monday's game against the Cubs. He then entered the game as a pinch-hitter in the ninth inning and remained in the game to play right field.

"I'm nowhere near the pain that I had yesterday," Harris said. "I was telling the trainers, 'It's amazing what one day of treatment can do.' It was the most pain, I've ever been in. Normally I wouldn't say anything. I try to fight through it, but I had to let the trainers know. I didn't want to hurt the team and I don't want to hurt myself. I'm feeling better, though."

Harris originally hurt the knee on April 10 against the Mets. In the ninth inning of that game, he made a great diving catch to end the contest, securing a 4-3 victory for the Nats. It turned out that his spikes were caught on the ground when he made the catch. He didn't feel pain in the knee until the next morning.

Harris then reinjured the knee Saturday after making two great catches against the Dodgers. Harris had an MRI on the knee, which revealed inflammation.

With left-handed pitchers going for the Cubs in the first two games, Harris hopes to start against right-hander Ryan Dempster in Wednesday's finale.

Zimmermann, Flores on mend

CHICAGO -- It appears right-hander Jordan Zimmermann and catcher Jesus Flores could be back on the field soon.

Zimmermann, who is on the disabled list because of right elbow reconstruction, is throwing live batting practice. General manager Mike Rizzo said Zimmermann is ahead of schedule, but he isn't expected to participate in a rehab assignment until sometime in August.

Catcher Jesus Flores, on the DL with a right shoulder injury, is swinging the bat, but Rizzo didn't give a timetable when he will return to action.

Nats may need to make a move

With three position players hurt [Willie Harris, Ryan Zimmerman and Ivan Rodriguez ] and none of them on the disabled list, the Nationals have not ruled out calling up a position player from the Minor Leagues. But that would mean taking a reliever off the 25-man roster. They currently have seven relievers on the roster. Riggleman said the team is not in a rush to make such a move.