Zambrano was suspended by the team for three games after his dugout tirade last week. The right-hander is set to be evaluated in New York on Wednesday by doctors mutually agreed upon by Major League Baseball and the players' union.
The Cubs expect to be without Zambrano through the All-Star break.
Grabow is out after spraining his left knee Monday. He was on the 15-day DL earlier this month with the same trouble.
The Cubs called up left-handed reliever James Russell and right-handed reliever Jeff Stevens from Triple-A Iowa on Tuesday.