Interim manager Chad Tracy said after Thursday's 4-3 win over the Rangers that Chapman was unavailable due to a lat issue, Tim Healey of The Boston Globe reports.
Chapman has been dealing with the issue for a couple days, and Tracy said the Red Sox will be "conservative" with the left-hander. With Chapman unavailable Thursday, Garrett Whitlock came on for the save, his fourth of the season. Chapman hasn't pitched since Sunday, when he walked two and struck out three in an inning of work against the Royals to secure his 34th save of 2026.