Dodgers ace Clayton Kershaw threw a 15-pitch bullpen session on Sunday to test his injured back and will throw another session on Tuesday in Houston, manager Dave Roberts said after the club’s 3-1 loss to the Giants.

Kershaw, who went on the 10-day injured list Thursday with back stiffness instead of pitching Opening Night, is dealing with a back injury for the fourth time in his career. In the three previous stints, he’s been out 10, five and three weeks. Kershaw said he was injured in the weight room doing core exercises.

Kershaw missed his second consecutive Opening Day start against the Giants, after missing last year’s opener with a sore shoulder. Despite that, he went 16-5 with a 3.03 ERA and made 28 starts.

Dustin May started Opening Night for Kershaw and allowed one run in 4 2/3 innings. May is scheduled to take Kershaw’s place again as the Wednesday night starter in Houston.