PHILADELPHIA -- Stephen Strasburg is expected to make his next start.

And that, Nationals manager Davey Johnson said, is all he's concerned about.

Strasburg left his start Sunday after five innings with what was described as tightness in his right biceps. That naturally attracted a lot of attention since he's one of the best young pitchers in baseball. But Johnson suggested Monday that any worries may have been exaggerated.

"I wasn't really concerned that much after he came out. I thought it was normal tightness," Johnson said. "But anything at all with him, everything with him is magnified. He's going to make his next start, and that's all I know."

Johnson added that he would have reacted the same no matter who the pitcher had been.

"Anybody in my rotation, anybody in the 'pen, anybody who has anything bothering them. End of conversation," he said.

Mattheus unavailable with discomfort in foot

PHILADELPHIA -- Right-handed reliever Ryan Mathheus experienced discomfort in his left foot while running in the outfield before Monday night's game and was not available to pitch.

Mattheus had an X-ray and was expected to visit the Nationals' foot specialist in Baltimore on Tuesday. Manager Davey Johnson said he hoped the right-hander would be back for Tuesday night's game.

"He thinks something might have broken up in there that's been bothering him for two weeks," the manager said. "He came in and iced it, and we're treating that just like anybody who's got something wrong. Look at it 10 ways from Sunday."

Right-hander Chien-Ming Wang, who is on the disabled list with a strained left hamstring, is scheduled to throw on the side at Citizens Bank Park on Tuesday. It's possible that, if Mathheus had to go on the DL, Wang could be activated to take his spot on the roster.

Lidge cleared to begin throwing off mound

PHILADELPHIA -- Nationals reliever Brad Lidge was examined by Dr. William Meyers, who performed the surgery to repair his sports hernia on May 1, and was cleared to begin throwing off a mound.

Lidge said he will throw a light bullpen session on Wednesday, then fly to Viera, Fla., to continue his rehab at the Nationals' Spring Training facility. If all goes well, he should be able to begin a rehab assignment after a few more bullpen sessions. The target date for him to be activated is June 15, although he said he hopes to return sooner.

"I feel good. It's surprising how good you can feel in three weeks," Lidge said. "Any time you have to have surgery it's horrible. But at least this one's quick."

The closer for the Phillies' 2008 World Series championship team, Lidge worked out at Citizens Bank Park much of the offseason before being signed as a free agent by Washington.

"At that time, I was still a Phillie in my mind. So it's only been a few months since anything's changed. It really doesn't feel like I've been gone that long," Lidge said. "I felt like I had a spot here. My thought was that, in the end, I would take pretty much whatever [the Phillies offered], no matter what that was. But there was no contract offer.

"It was disappointing. But at that point, you're just collecting the pieces and saying, 'All right, now where do I go?' You're forced to turn the page quickly. There's no time to sit and sulk. And fortunately, I landed on a really good team."

Lidge added that it was "cool" to be back. He stopped in the Phillies' clubhouse before the game to say hello to his former teammates.

"It's great to see the guys on the other side," Lidge said. "This is an incredible place to play baseball."

Harper embraces challenge of playing in Philly

PHILADELPHIA -- The storyline coming into Monday's game between the Nationals and Phillies revolved around the reception rookie phenom Bryce Harper would receive from the notorious Philadelphia fans, especially after the incident at Nationals Park on May 6 in which Phillies starter Cole Hamels nailed him with a fastball. The left-hander later admitted he hit Harper on purpose and was suspended for five games.

Harper said he wasn't even thinking about that, but many in the sellout crowd apparently were. He was booed each time he came to the plate, but took it all in stride. He even pointed out that he's played against Phillies farm teams during his quick trip through the Minors.

"[Their fans] boo at every level," he said with a laugh.

In fact, the 19-year-old rookie insisted Philadelphia is one of the cities he had been looking forward to playing in.

"You're playing in a place where Mike Schmidt and guys like that played," Harper said before the game. "It's going to be a lot of fun in here. They have a great fan base, and we're going to come in here and try to prove some people wrong.

"Philly has always had a great history in all their sports. Tommy McDonald with the Eagles, [Julius Erving] with the NBA -- you have so much history in this sport and so much history in all the other sports in this place, so it's going to be a lot of fun playing here."

Harper singled his first two times up against Phillies starter Kyle Kendrick. In the fourth inning, he also stole second and scored on Ian Desmond's RBI single.

Worth noting

• Nationals first baseman Mike Morse, who is on the disabled list with a left lat strain, reported to extended spring training in Viera, Fla., on Monday and is scheduled to begin hitting Tuesday.

• The Nationals have beaten the Phillies in eight of the last nine meetings.

• Shortstop Ian Desmond, who hit his seventh home run to give the Nationals a 1-0 lead in the second inning, has hit safely in 10 of his last 11 games.