The Red Sox will be without one of their two set-up men in the bullpen for at least a couple of weeks.

The Red Sox announced Friday prior to their series opener against the Kansas City Royals at Fenway Park that they placed reliever Justin Slaten on the 15-day injured list with right elbow inflammation. The move is retroactive to July 9 and Boston recalled lefty Cam Booser to take Slaten's spot on the active roster.

"He's been grinding through it probably the last 15 days so he wasn't able to bounce back from the last one in New York so I think it's smart to put him on the IL, " Red Sox manager Alex Cora told reporters, per MLB.com's Ian Browne. "It's retroactive to, what, two days ago, three days ago. We've got the All-Star break and hopefully he'll be back right after the Dodgers series. It's his first time pitching this much and obviously we've got to be careful with him."

Slaten, who the Red Sox traded for this past offseason after the New York Mets took him in in the Rule 5 draft, has been a critical piece in Boston's bullpen during his first season in the big leagues. The 26-year-old right-hander is tied with Chris Martin for the team lead in holds with 10 while also posting a very respectable 3.38 ERA and 1.05 WHIP. He also recorded 45 strikeouts in 42 2/3 innings to go along with just nine walks.

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Slaten last pitched on Sunday when he worked a scoreless inning of relief at Yankee Stadium to bridge the gap to closer Kenley Jansen.

Booser has frequently shuttled back-and-forth between Triple-A Worcester and Boston recently. He was just optioned to Worcester on July 8 after his second stint this season with the Red Sox, but didn't stay there long due to Slaten's injury.

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Booser will give the Red Sox another left-handed arm in the bullpen to go along with Bailey Horn and Brennan Bernardino. Booser owns a 3.00 ERA with 34 strikeouts in 30 innings with the Red Sox.

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