Schwarber, 24, is hitting .171 just seven months after helping the Cubs to a World Series victory. Chicago is in second place in the National League Central.
As part of a series of moves, the Cubs will also put outfielder Jason Heyward on the disabled list with a cut on his hand, a source said. They are calling up outfielder Mark Zagunis from Iowa for his first taste of the majors. Pitcher Dylan Floro is also rejoining the team.
After losing Dexter Fowler to free agency, manager Joe Maddon installed Schwarber in the leadoff spot to start the season. That lasted 36 games before he was dropped in the order and played against only certain right-handed pitchers. He hit .143 against lefties before being sent down.
Schwarber hit .412 in the World Series last season with a .500 on-base percentage after missing all but three games of the regular season because of a serious knee injury. He was never cleared to play in the field, so he served as designated hitter for World Series games in Cleveland.
He was the fourth pick in the 2014 draft before making his debut for the Cubs in 2015.