Chris Martin’s absence was noticeable on Thursday, when the Red Sox needed 12 innings and five relievers to complete their sweep of the Marlins in Miami.

Before Friday night’s series opener against the Yankees, manager Alex Cora explained why: Martin has been placed on the 15-day injured list with “right-elbow inflammation.”

It’s been a difficult season for the Red Sox setup man; Friday marks one month exactly since the club placed him on the 15-day IL due to anxiety. Since being activated on June 19, he’d looked like his usual lock-down self, making five scoreless appearances with four hits, zero walks, and five strikeouts.

Though Cora told reporters at Yankee Stadium that he doesn’t think the injury is serious, elbow issues must be handled with caution. Martin has been key to Boston’s success this season; he owns a 3.42 ERA over 26 games, with 29 strikeouts and just two walks over 26.1 innings, and the Red Sox are 18-8 when he pitches.

To fill his spot on the active roster, the Red Sox have recalled left-hander Cam Booser from Triple-A Worcester.