Today's move comes one day after the team optioned fellow right-hander Billy Petrick to Iowa.
It's Gallagher's second stint with the Cubs this season. He has no record and a 9-point-53 E-R-A in three relief appearances. He made his major league debut on June Ninth at Atlanta.
The 23-year-old Petrick was originally called up from Double-A Tennessee on June 26th. He has no record and a 3-point-18 E-R-A in four relief appearances with the Cubs.
He hasn't yet pitched at Triple-A this year. He went 1-and-1 with two saves and a 2-point-37 E-R-A in 18 games with Tennessee.