To take his place on the roster, the team activated right-hander Cody Stashak, who was on the IL with right biceps tendinitis.
Manager Rocco Baldelli said before Sunday's game at Fenway Park that he doesn't think Gray will miss more than one start.
Gray (0-1), 32, allowed a homer to Alex Verdugo in the second inning before being pulled two batters later with right hamstring tightness in Minnesota's 4-0 loss. Gray was acquired from the Cincinnati Reds in a trade last month.
The veteran appeared to stumble at the bottom of the mound while following through on a pitch during that inning. When Baldelli and the training staff made it to the mound to check on him, the broadcast's television cameras clearly showed Gray tell them "hamstring."
The Twins are the fourth major league team for Gray, who began with the Oakland Athletics before stops with the New York Yankees and Reds. In his last season with Cincinnati, he was 7-9 with a 4.19 ERA. Minnesota has high hopes for Gray, who is 82-73 in his career and has appeared in two All-Star Games (2015, 2019).
"This is an elite guy, as a pitcher and as a person to join our group in our clubhouse," Baldelli said last month. "You couldn't ask for anything more from an addition."
The Associated Press contributed to this report.