Gray, 32, left Sunday's game against the Kansas City Royals in the seventh inning. He is 3-1 with a 2.41 ERA in seven starts for the Twins this season.
He also missed 19 games earlier this season with a right hamstring strain.
In a related roster move, the Twins called up pitcher Yennier Cano, who made his major league debut on May 11. The reliever has allowed 11 runs on 12 hits in 7⅓ innings.