The Cubs released right-hander Edwin Jackson on Monday, one week after he was designated for assignment.
Jackson was 2-1 with a 3.19 ERA in 23 relief appearances for the Cubs this season.
Signed to a four-year deal worth $52 million before the 2013 season, Jackson struggled badly over his first two years with the Cubs, going 14-33 with a 5.58 ERA and was moved to the bullpen near the end of last season.
Chicago also announced right-hander Dallas Beeler will start Tuesday.
Beeler has started twice for the Cubs this season and has no record with a 6.43 ERA.