Craig Stammen's season potentially ends with torn flexor

Nationals manager Matt Williams announced today that right-hander Craig Stammen has a torn right flexor that will require surgery. The injury could potentially force Stammen to miss the remainder of the season.

"It depends on the extent of the damage and the rehab, but it's possible," said Williams. "We'll see."

Stammen led the Nationals in appearances this season with five before experiencing right forearm stiffness that sent him to the 15-day disabled list Wednesday. He pitched four scoreless innings, allowing two hits and three walks with three strikeouts over the first nine games.

"It's never great to lose one of your main pitchers," said Williams. "He adds a lot of value to our club. He pitches in many different roles. But we'll just have to have somebody step up and fill those roles. It's unfortunate for him because he works really hard. So we have to get it fixed and get him back out there as quickly as we can."

The Nats brought up left-hander Felipe Rivero to join the bullpen today. He's given up three runs in 2 2/3 innings at Triple-A Syracuse this year.

"He's powerful," said Williams. "We put him in the relieving role over his last six or seven times on the mound. Three at the end of spring training, couple more in the minor leagues. He's gone back to back down there, so we feel confident in that regard. What he's shown us is he's thrown the ball over the plate, mid-90s fastball with breaking ball and changeup. And we need another lefty, so he's a logical option for us. Power lefty out of our 'pen."

The news is particularly tough for a Nationals bullpen that is already without right-hander Casey Janssen, who is still recovering from tendinitis in his throwing shoulder. Janssen is still in Viera, Fla., rehabbing without a defined timetable on his return.