The Cubs added a reliever today, but not the one you might have thought of:
#Cubs moves today: Signed LHP Jorge De La Rosa. Rosario to Iowa. Darvish to 60 day DL— Carrie Muskat (@CarrieMuskat) August 10, 2018
Jorge De La Rosa is a 37-year-old lefthander who's had a long career mostly with the Rockies and Diamondbacks. This year he had a 4.63 ERA and 1.600 WHIP in 42 games for Arizona covering 35 innings before he was released six days ago.
Lefthanded hitters are hitting .220 against him this year, so if he can get LHB out, he can still be yseful.
Randy Rosario will certainly be back in September, if not before.
The move of Yu Darvish to the 60-day DL is simply procedural, to make room for De La Rosa. The 40-man is full; if and when Darvish is activated, someone else will have to be removed.