Outfielder Junior Lake was optioned to Iowa and right-hander Anthony Varvaro was designated for assignment Wednesday. Varvaro was claimed off waivers from Boston on Sunday and added to the 25-man roster Tuesday but did not pitch.
Grimm (right forearm inflammation) made one rehab appearance with a scoreless inning Monday for Iowa at Nashville. Grimm made the opening day roster for the second straight season but had not pitched in the majors this year.
Grimm was 5-2 with a 3.78 ERA in 73 relief appearance last year with Chicago in his first full season in the majors.
This is the second call-up this season for Szczur, who made the opening day roster and was optioned to Iowa on April 19.