The Nationals placed struggling left-handed reliever Doug Slaten on the 15-day disabled list today, replacing him in the bullpen with right-hander Craig Stammen, whom they recalled from Class AAA Syracuse. Stammen will arrive shortly before tonight’s, but will not be available to pitch, since he pitched seven innings in a start two days ago.

Manager Jim Riggleman expressed concerned over Slaten’s health Friday night, after Slaten continued a rocky season by allowing a bases-loaded triple to the only batter he faced. Slaten insisted he was fine, but today admitted he has felt shooting pain in his forearm and elbow for roughly two weeks. The official diagnosis is ulnar neuritis, which is irritation in the ulnar nerve.

About 10 days, Riggleman shut Slaten down for four games. Slaten insisted he could pitch, but Riggleman worried.

“Just the way he was not attacking the strike zone indicates he wasn’t fine,” Riggleman said. “He’s experiencing some things that are just not typical of Doug. He’s not throwing strikes. He’s not getting ahead of hitters. He’s better than that.”

Slaten will receive an MRI. It’s not clear when he will be able to return to the Nationals. Without him, the Nationals have only one left-hander, Sean Burnett, in their bullpen, which Riggleman does not see as an issue. “We’ve never been really locked in to have one lefty,” he said. “You just try to put the best pitchers you can out there. I think we’ll be fine.”

Last year, Stammen began the season in the Nationals’ rotation and made 19 starts before heading to the bullpen and appearing in 16 games. Stammen, now 27, went 4-4 with a 5.13 ERA. He began this year in Syracuse and has pitched only as a starter.

Stammen’s promotion seemingly raised the possibility of him replacing Yunesky Maya in the starting rotation. Riggleman, though, remained committed to Maya starting June 8, the next time his turn comes up in the rotation. He said Stammen will be considered a reliever only, at least for now.

Twice this season, the Nationals recalled Collin Balester from Syracuse when they needed a bullpen arm. This time, Nationals officials, including General Manager Mike Rizzo, director of player development Doug Harris and Syracuse coaches, decided Stammen was the best pitcher available for the bullpen role.