Pittsburgh Pirates All-Star closer Jason Grilli left Monday's game against the Washington Nationals in the ninth inning because discomfort in his right forearm.
With two outs and an 0-1 count on pinch-hitter Steve Lombardozzi, Grilli threw a pitch that Lombardozzi fouled off.
The pitch left Grilli in obvious pain, and he left the game with the trainer.
Grilli was replaced by Vin Mazzaro, who got the final out in the Pirates' 6-5 victory.
The severity of Grilli's injury was not immediately known.
"We will wait and see how he feels tomorrow. That is the hard part of things that can happen," manager Clint Hurdle said. "Our roster is going to be fine."
Grilli, 36, leads the National League in saves with 30 and has a 2.34 ERA. He recently was on the All-Star team for the first time and was on the cover of Sports Illustrated.
If Grilli is out for a significant period, the Pirates may use Mark Melancon as their closer.