Jon Niese (3-5, 4.40) was scheduled to pitch Saturday. The Mets will move him back to Sunday's game.
The Nationals and Mets will make up Thursday's postponed game on July 26. They will play a split doubleheader with the makeup game beginning at 1:35 p.m. ET before the regularly scheduled game at 7:05 p.m. The two games will require separate admission. Fans with tickets to Thursday night's game may exchange them for any remaining regular or value home game during the 2013 season.
Weather could remain a problem for the Mets and their pitching staff as heavy rain and thunderstorms are forecast for the New York area on Friday.
Collins talked before batting practice on Thursday about why caution is important on nights when the weather is shaky, an issue that could come up again Friday involving Harvey.
"It's really difficult to maneuver your pitching around the weather when it may not rain," Collins said. "You've just got to deal with it. Certainly the one thing we don't ever want to do is start those guys, start Matt or Jon or anybody else to where they give you three innings, and here comes the big storm. And now they're done."
Collins also said during Thursday's pregame talk about how the team's lack of offense -- their .228 average is next-to-last in the National League -- has held down Harvey's win total.
"[It's a] function of what's going on," Collins said. "Like I said the other day, he should have nine [wins]. He doesn't, so he's got to keep pitching well."
Harvey comes into the game as the first pitcher to remain undefeated through his first 12 starts of the season in franchise history. Dillon Gee was the last Mets pitcher to begin a season at least 5-0. He went 7-0 to begin the 2011 season.
Jeff Seidel is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.