Between games of Monday’s doubleheader, the Red Sox announced they have activated right-hander Justin Slaten from the 15-day injured list, optioned right-hander Josh Winckowski to Triple-A Worcester and added left-hander Bailey Horn as the club’s 27th man.

Slaten has been on the IL since July 9 with right elbow inflammation, and prior to that the rookie had been one of Boston’s best relievers. The Rule 5 pick has posted a 3.38 ERA and 45 strikeouts in 42.2 innings, and his return should provide a massive boost to a bullpen that has struggled significantly in his absence.

Winckowski has recorded a 4.37 ERA in 59.2 innings over 30 appearances for Boston this season. He pitched in the first game of Monday’s doubleheader, throwing a scoreless ninth inning in the Red Sox 4-1 loss.

Horn’s elevation will give the Red Sox two left-handers in the bullpen Monday night. In 14 big league games this season he has posted a 6.48 ERA in 16.2 innings.