Yu Darvish
On November 3, 2017, Rosario was claimed off waivers by the Chicago Cubs. He began the season with the Iowa Cubs. In mid-May of the 2018 season, Rosario was recalled twice and sent down to the minors twice before he received a third recall to replace the injured Yu Darvish. He pitched 7 2/3 innings of relief allowing only 2 hits and had a 2-0 record. Rosario was designated for assignment on September 9, 2019.