Kelvin Herrera has been closing games for the Nationals while Sean Doolittle works back from injury. (Nick Wass/Associated Press)

With closer Sean Doolittle already on the disabled list, the Nationals’ bullpen might have lost its interim closer to injury Tuesday night when Kelvin Herrera walked off the mound with trainer Paul Lessard in the middle of a ninth-inning debacle. Dave Martinez had summoned Herrera to pitch the ninth in a 1-1 game, and he allowed four line drives on six pitches — three of them for hits that gave the Braves a two-run lead.

After the game, Martinez said Herrera had tightness in his throwing shoulder and is scheduled for an MRI exam Wednesday morning. The 28-year-old reliever said he has never felt that type of discomfort.

“I couldn’t finish my pitches,” Herrera said through team interpreter Octavio Martinez. “I felt like I was aiming them instead of throwing them.”

Herrera showed no obvious trouble while pitching, besides his results, before Martinez and Lessard headed out to check on him. After weeks of shaky outings, Herrera finally compiled a dominant, 1-2-3 ninth inning in the Nationals’ one-run win over the Reds on Sunday. But since the Nationals acquired him from the Royals in mid-June, Herrera has flexed and shaken his throwing arm frequently between pitches — something easily dismissed as mannerism for a new player on a new team or easily reinterpreted as a sign of trouble when something happens like it did Tuesday night. When Martinez saw him do it in the middle of that inning, he chose the latter interpretation.

“His ball was coming out okay, but when I saw him [shake his arm] I thought there was something wrong,” Martinez said. “… He said his shoulder was tight. I said, ‘That’s it, you’re done.’ He said, ‘Well …’ I said, ‘You’re done.’ ”

Herrera’s numbers have regressed with the Nationals, though he was due for some regression after an outstanding first few months with the Royals. Though his velocity has not dipped, his command has not been sharp. His WHIP with the Nationals is double what it was with Kansas City. He walked two batters in 25 2/3 innings with the Royals. He has walked eight in 17 2/3 innings with the Nationals.

Though those numbers raise fair questions about an underlying issue, Herrera and his manager said the trouble was new. Herrera said he didn’t feel it until he was taking his warm-up tosses on the mound before the inning. He said after the game he couldn’t evaluate his concern level yet. An MRI exam will give him more information.

Still, even if that exam shows no major issues, the Nationals seem likely to place Herrera on the disabled list out of caution. If they do need to call up a reliever to replace him, Koda Glover — long thought to have the makeup and stuff of a future closer — is healthy and pitching well for Class AAA Syracuse. Trevor Gott, Austin Adams and Tim Collins also are pitching for the Chiefs and have all had experience in the big leagues this season.

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