The Red Sox made the move retroactive to Tuesday. Sam Travis will be added to the roster Saturday.
The 25-year-old right fielder is hitting .359 and also has scored a majors-best 52 runs. He ranks among the leaders with 17 home runs, 37 RBI and 13 steals.
Betts didn't play Thursday night in the series opener against the Astros, the fifth straight game he'd missed because of soreness on his left side.
Manager Alex Cora had said he didn't think Betts would need to go on the DL, and had hoped to have him in the lineup before the series ends Sunday.