The Red Sox got back a key member of the bullpen on Wednesday, but they’ll be without one of their biggest bats for a little while longer.

Red Sox manager Alex Cora told reporters in Kansas City that Tyler O’Neill is headed to the 10-day injured list. The outfielder had missed the last four games due to illness but is now also battling an infection in his left calf.

The Red Sox also activated right-hander Chris Martin from the IL, called up infielder Enmanuel Valdez and optioned left-hander Cam Booser to Triple-A. Cora also said right-hander Nick Pivetta will miss his next start so he can get additional rest after seeing his velocity plunge in his most recent outing.

Cora told reporters that O’Neill shouldn’t be out long and that he should hopefully be back after the minimum 10 days. O’Neill has been one of Boston’s best right-handed hitters, batting .268 with 22 home runs and a .900 OPS in 80 games.

Valdez is a left-handed hitter and his big league numbers on the season don’t stand out, but over his last 11 MLB games from June 19 to July 11 he batted .313 with an .826 OPS, and he has nine home runs and an .803 OPS on the season at Triple-A.

Martin has been out since July 3 with right elbow inflammation, but when healthy the 38-year-old has been one of Boston’s top bullpen options. The right-hander currently boasts a 3.42 ERA in 26.1 innings, and he’s recorded 10 holds as the club’s primary eighth-inning set-up man.

Booser has also been a strong contributor to the Red Sox bullpen this season. The 32-year-old rookie has posted a 2.77 ERA in 39 innings after toiling in the minors and the independent scene for more than a decade. He was also one of Boston’s few reliable relievers during the bullpen’s disastrous two-week stretch to start the second half, posting a 2.25 ERA in 10 appearances at a time when most of the club’s other relievers were coming unglued.

He also likely wouldn’t have been available Wednesday after throwing 21 pitches on Tuesday to cap off his fourth appearance in five days, making him the odd man out as the Red Sox looked to add a fresh arm.