The Cubs swapped bullpen pitchers ahead of Monday night's series-opener with the visiting San Francisco Giants at Wrigley Field.
Zac Rosscup was called up from Triple-A Iowa, with Dylan Floro heading back to Des Moines.
To make room for Rosscup on the team's 40-man roster, pitcher Jake Buchanan was designated for assignment.
The Cubs' oft-utilized relief corps ranks fourth in the National League in innings pitched, with 158.1 frames tossed by bullpen pitchers. That workload has made reinforcements from the minor leagues commonplace.
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Floro pitched two innings in Sunday's win over the Milwaukee Brewers, yielding five runs in the ninth inning of what ended up a blowout 13-6 Cubs victory.
It was his second appearance of the season after his 4.1-inning outing in a May 9 loss at the Colorado Rockies.
MLB
Rosscup joins the Cubs for the first time since 2015. He made zero major or minor league appearances last season after posting a 4.39 ERA in 26.2 innings of work during the 2015 campaign.
This season with Iowa, Rosscup turned in a 3.45 ERA in 15.2 innings of work.