The Chicago Cubs placed closer Adbert Alzolay on the 15-day injured list Monday with a forearm strain and called up their top prospect, outfielder Pete Crow-Armstrong.
The Cubs also activated reliever Michael Fulmer from the IL before the opener of a three-game series at Colorado.
The loss of Alzolay is a big blow for Chicago, which is fighting for playoff positioning in the NL standings. Alzolay has been the team's most dependable reliever, going 2-5 with a 2.71 ERA and 22 saves in 25 chances during a breakout season.
The 21-year-old Crow-Armstrong, meanwhile, is ranked 15th in ESPN prospect guru Kiley McDaniel's latest top 50 prospects.