The Philadelphia Phillies placed ace Zack Wheeler on the 15-day injured list Saturday with a blood clot in his right arm, the team announced Saturday. The announcement was made following the team's 2-0 loss to the Washington Nationals.

Dave Dombrowski, the president of baseball operations for the Phillies, said Wheeler had been diagnosed with a "right upper extremity blood clot."

"There's not a lot that we can say on it at this time," said Dombrowski, who commended doctors for finding the clot. "It could have been a much more trying situation than it is."

Phillies head athletic trainer Paul Buchheit said Wheeler had been feeling better after some right shoulder soreness, but that changed Friday.

"He felt a little heaviness," Buchheit said. "So, the doctors here were great in helping to diagnose and expedite that diagnosis this morning."

Buchheit said he didn't think Wheeler's present condition had anything to do with his previous stiffness. He said there is a wide variety of treatments available, but declined to get into specifics.

Dombrowski said Wheeler would be evaluated further in Philadelphia.

Wheeler pitched Friday against Washington and was limited to five innings for the second consecutive start. The right-hander allowed two runs and four hits.

The 35-year-old Wheeler is 10-5 this season with a 2.71 ERA. He has 195 strikeouts in 149 2/3 innings.

Wheeler's absence comes as right-hander Aaron Nola is set to return from the injured list Sunday in the series finale against the Nationals. The 32-year-old has been sidelined since May as he recovered from a sprained ankle and fractured rib.

On Thursday, Phillies manager Rob Thomson said the club will shift to a six-man rotation.

Closer Jhoan Duran, who exited Friday's 6-2 win after taking a comebacker off his right ankle, is expected to be OK.