Bush is set to be evaluated in Milwaukee by Dr. William Raasch on Friday. He pitched three innings and allowed five earned runs for Double-A Huntsville on Wednesday.
"It's fairly disappointing," Brewers manager Ken Macha said. "But you have to deal with your injuries."
Bush has been on the disabled list since June 23 with a micro-tear of his right triceps muscle. In his first rehab start for Class A Wisconsin, he threw 4 2/3 innings and allowed four hits and one unearned run. This season he is 3-4 with a 5.67 ERA.
Macha said right-handed starter Mike Burns would continue to start in Bush's spot. Burns is 2-2 with a 5.54 ERA in four starts.
"Burns has done a good job for us," Macha said.
Steve Gartner is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.