The Nationals, who have lost three games in a row for the first time in a month, will counter with right-hander Jordan Zimmermann.
Zimmermann's 2.54 ERA is the second-lowest mark in the National League this season, and he has pitched like the ace of the Nationals' staff.
Earlier this month, however, he experienced some soreness in his right shoulder. Manager Davey Johnson said that as far as he knows, the problem has cleared up for his right-hander, but the skipper won't push Zimmermann too hard in late August.
"I'm gonna loosen him up a little bit, but I'm still not gonna extend him too much -- any of [the pitchers] -- at this point in the season," Johnson said.
Lee has also pitched well this season, leading the Major Leagues in strikeouts-to-walks ratio, but has little to show for it in his record. He is 2-7, and the Phillies have won just seven of his 22 starts.
The former Cy Young Award winner characterized it as a "strange" year.
"I really don't care about my numbers, to be honest with you. I just care about winning," Lee said. "It's just been one of those years. Usually there's a guy on each team that things don't really go his way, and that happens to be me this year. I'm not going to make excuses or feel sorry for myself."
Sunday could be the boost Lee has been looking for. Throughout his career, he has pitched well against the Nationals, the franchise that originally drafted him in 2000 when they were still in Montreal. Of Lee's six career starts against the Nationals, he hasn't allowed a run in three of them.
Nationals: Morse, Desmond remain day to day with injuries
The Nationals were without left fielder Michael Morse and shortstop Ian Desmond in Saturday's 4-2 loss to the Phillies. Both are considered day to day and will miss Sunday's series finale against the Phillies.
Morse was hit on the right hand by a Kyle Kendrick pitch in the first inning Friday night and said it hurt to grip a bat Saturday. Desmond missed both Friday and Saturday's games with a sore right hamstring. Desmond had only just returned to the lineup a week ago after missing 26 games with an oblique injury.
Without Morse and Desmond, the Nationals scored just two runs Saturday for the second straight game.
Phillies: Brown, Polanco ailing
Outfielder Domonic Brown did not start Saturday's game against the Nationals, marking the first time he was out of the Phillies' lineup since his callup from Triple-A Lehigh Valley on July 31. Brown pinch-hit in the seventh inning, striking out against Ryan Mattheus.
Third baseman Placido Polanco was out of the lineup for the third straight game with a sore back, the same injury that forced him onto the disabled list for a month. Polanco returned from the disabled list Monday but has had just nine at-bats in four games since then. Manager Charlie Manuel did not rule out a return to the DL.
"He says he doesn't want to go on the DL, but at the same time, we also need a player on the bench," Manuel said. "If I send one guy to pinch-hit early, all of a sudden we're short on the bench. We need all 25 of our players. ... If it hurts him and it hurts his performance and it hurts him to play, then it's not good for him or us."
After Saturday's 4-2 loss, the Nationals are 5-6 against the Phillies this season. Washington has winning records against the other three NL East teams.
Phillies left fielder Juan Pierre is one stolen base shy of tying former Dodgers shortstop Maury Wills for 19th most all time. Pierre has 585 career stolen bases.