The Cubs are down to one lefty in their bullpen after they placed veteran Daniel Norris on the 15-day injured list Thursday with a sprained left index finger.
Adrian Sampson was recalled from Triple-A Iowa in a corresponding move.
Norris, who holds a 7.24 ERA in 24 appearances this season, has struggled in June, holding a 9.58 ERA across nine appearances/10 1/3 innings.
He allowed four runs in his most recent appearance on Wednesday, all of which were unearned.
Sampson threw 4 1/3 shutout innings in relief Sunday vs. the Braves, allowing one hit while striking out five. The Cubs optioned him to Iowa Monday as MLB's 13-pitcher limit on active rosters went into effect.
"That's as good as I've seen him," manager David Ross said of Sampson's outing.
This marks Sampson's third stint with the Cubs this season. He made one appearance in May before being designated for assignment.
The Mariners claimed him off waivers and DFA'd him soon after, and he then rejoined the Cubs organization on a minor-league deal.