PHILADELPHIA — Phillies ace Zack Wheeler had surgery Monday to remove a blood clot in his upper right arm, and the team says a timeline for his recovery remains unknown.

Manager Rob Thomson acknowledged the uncertainty, saying, “We don’t know,” when asked whether Wheeler would pitch again this season, or if the situation was career-threatening.

The Phillies said Wheeler underwent a thrombolysis procedure by Dr. Paul DiMuzio at Thomas Jefferson University Hospital.

Wheeler, 35, a three-time All-Star who leads the majors with 195 strikeouts, was placed on the injured list Saturday after experiencing worsening shoulder “heaviness” following his start in Washington the previous night.

His condition fell under the realm of thoracic outlet syndrome, a known risk for overhead-throwing athletes, where compressed blood vessels or nerves near the neck can lead to clot formation.

Treatment options vary depending on the root cause. In addition to clot-dissolving procedures, athletes often undergo extended blood thinner therapy — spanning months — or even rib resection surgery to prevent recurrence, with high return-to-play rates in cases where such interventions are successful.

Meanwhile, the Phillies are left without the anchor of their rotation with six weeks to go in the regular season. The National League East leaders are leaning on a group of pitchers, including Cristopher Sánchez, Ranger Suárez, Taijuan Walker and Jesús Luzardo, to fill the void. Aaron Nola, who missed three months because of ankle and rib injuries, returned to the rotation on Sunday.

“You could always rely on [Wheeler] every fifth day, but at the same time, I have confidence in our entire rotation,” Thomson said. “As tough as it is to lose Zack, I feel really good about our staff. I really do.”

In 24 starts this season, Wheeler is 10-5 with a 2.71 ERA. He has thrown at least 192 innings in three of the previous four seasons.

Beyond the immediate baseball implications, teammates have rallied around Wheeler.

“He’s the heart of this team, the heart of the staff … you never want to see it,” reliever Matt Strahm said, emphasizing that Wheeler’s health is everyone’s priority.