When he dominated in his rehab start on Wednesday, Garrett Whitlock looked like he was on the cusp of rejoining the Red Sox starting rotation.

Instead, the right-hander has been shut down from throwing due to soreness in his pitching elbow, Alex Cora announced on Friday.

“Garrett felt soreness around the elbow area (yesterday), so we’re gonna shut him down for now, see what’s going on this weekend and we’ll know more on Monday,” the manager told reporters in St. Louis. “That’s where we’re at. He felt great throughout the (rehab) outing. During the night, felt really good, and then yesterday he was doing okay and then we stretched him out, he was tight and he was sore, so that’s where we’re at.”

Whitlock will undergo tests in Boston over the weekend, while the team plays a three-game set with the Cardinals.

It’s a difficult blow for the righty, who’s dealt with a plethora of injuries over the last two seasons. After a dominant rookie campaign with the Sox in ’21, he endured five different IL stints in the subsequent two seasons, including season-ending hip surgery two years ago. Coming into spring training healthy, he pitched his way into the rotation, then posted a 1.96 ERA with 17 strikeouts over his first four starts of the season (four earned runs, 18.1 innings) before going on the injured list on April 17 with a left oblique strain.

“One thing about this kid, he’s resilient, he’s strong, he has been through worse,” Cora said. “Hopefully, it’s nothing, but we have to wait and see. In the meantime, we’ll stay the course with the same guys in the rotation and keep going.”

The ripple effect of this Whitlock development is significant. In the immediate future, Tanner Houck won’t get an extra day of rest after all; he threw a career-high 113 pitches in his most recent start, and Cora was hoping Whitlock’s return would enable him to push back the rest of the rotation by a day. Moreover, for now the Red Sox don’t have to decide whether or not they want to carry a six-man rotation, and Cooper Criswell still has a place in it.