Wheeler was placed on the 15-day injured list Thursday due to right forearm tendinitis, with the team announcing the move a couple of hours after interim manager Rob Thomson told reporters that Harper would come off the IL and play Friday.
Wheeler leads the Phillies in wins (11) and ERA (3.07) but had struggled of late, allowing 10 runs on 14 hits total in back-to-back losses to the New York Mets. The right-hander was slated to pitch Friday's series opener against the Pittsburgh Pirates but lefty Bailey Falter will now go in his place.
Phillies president Dave Dombrowski said Wheeler would miss two starts -- against the Pirates and next week on Philadelphia's trip to Arizona and San Francisco. No MRI has been scheduled to examine Wheeler's forearm, a sign that the Phillies are not overly concerned about the severity of the injury.
"We felt that it was better to deal with this right now and to get it over with,'' Dombrowski said.
The news Thursday was decidedly better on Harper, the reigning National League MVP who has been out about two months after his left thumb was broken by a pitch.
Thomson announced Harper's impending return from the injured list after consulting with the star.
"One, you get a great hitter back," Thomson said before a game against Cincinnati. "But he's also healthy. That's really important to us. To get another batter in that lineup makes a lot [of difference] ... everyone knows how great a hitter he is."
Harper was 5-for-8 with two home runs, two doubles and six RBIs in a two-game rehab assignment with Triple-A Lehigh Valley. His minor league stint was originally expected to last through the weekend but instead ended after a game-winning RBI double in the ninth inning Wednesday night.
"It all depended on how he felt seeing pitches, his timing and how comfortable he was in the box," Thomson said.
Harper took off Thursday to recover from some soreness, but he is set to be the designated hitter when the Phillies host Pittsburgh.
"His body was sore just in general, so it was like fifth day in spring training, which is understandable given he's been out for two months," Thomson said. "We told him to take a day and come here to work out. And we'll activate him tomorrow."
The two-time NL MVP was hitting .318 with 15 homers and 48 RBIs when a fastball from San Diego's Blake Snell on June 25 broke the thumb. He is likely to spend the rest of this season as Philadelphia's designated hitter since a small tear in the ulnar collateral ligament in his right elbow has kept him out of right field since April.
"It's huge because [pitchers] know where he's at all the time," Thomson said. "The same with Schwarber. They know where that guy is at all the time. So the guys in front of them tend to get more strikes and better pitches. Not all the time, but most of the time."
Information from The Associated Press was used in this report.