Dillon Gee, a 24-year-old righthander, is scheduled to make his major league debut in place of Santana at Nationals Park.
Santana was pulled from his start Thursday against the Atlanta Braves after the fifth inning when he reported experiencing tightness in the chest muscle. He had indicated he wanted to proceed with the outing against the Nationals on turn. General manager Omar Minaya said, however, that the organization would be conservative with Santana given the Mets' place in the standings.
"I wanted to go out and pitch," Santana said on Sunday. "... I could go, but they said no."
Santana tossed a shutout on short rest with torn meniscus cartilage in his left knee in Game No. 161 of the 2008 season with the Mets' postseason fate hanging in the balance. This discomfort pales in comparison, Santana indicated.
"If this was a different situation, no question, I'd be pitching," Santana said. "I know what pain feels like -- believe me -- and this is not even close to what it was back then. But I understand they want to be very careful. If that's the right thing to do, then we'll do it."
Santana threw a light bullpen session Sunday at Wrigley Field and said the muscle felt "all right," although he acknowledged a game would be more strenuous.
Following the bullpen session, Mets spokesman Jay Horwitz initially said Santana "feels fine," but there would be no decision until trainer Ray Ramirez talked to team doctors later in the day.
Manager Jerry Manuel had said before the session that Santana probably would be scratched if he felt even slight pain, adding the Mets "don't want to take any chances." He said Ramirez and the doctors would have the final say. Santana is 11-9 with a 2.98 ERA.
The ace planned to accompany the team to Washington, and did not foresee taking a detour to New York to see the team's medical staff unless the organization requested it. Minaya said there were no plans "right now" for Santana to see a doctor.
"It's a decision that they want to be very careful with everything, and I'll agree with it," Santana said. "I'm a competitor, and every time that I have a chance to go out there, I'm going to go out there. But, at the same time, it's a decision they made and I'm not going to go against it."
Said Minaya: "This late in the season and everything, we're encouraged that he had a good bullpen and all of that, but it's more to be cautious than anything else."
Minaya added there is no shoulder issue.
"It's the pec area, part of the chest," the GM said. "We just felt it was the safest way to go."
Information from the Associated Press was used in this report.