Keuchel, who's tied with Jarred Cosart for the team lead with eight wins, began experiencing the problem after throwing in the bullpen a few days ago. The Astros opted to be careful with the lefty, who's 8-5 with a 2.78 ERA and has been their top starter.
"He's been getting treatment the last few days," Astros manager Bo Porter said. "After thinking about it and talking about it, we felt like we'd rather be safe than sorry. He's been too valuable to us and is having such a great season, we don't want to risk him going out there anything less than 100 percent."
Oberholtzer had made nine starts for the Astros this year, going 2-6 with a 4.76 ERA, including 2-0 with a 2.08 ERA in two starts at the end of May before being sent down. He's 1-2 with a 4.65 ERA in five starts at Triple-A Oklahoma City.
Brian McTaggart is a reporter for MLB.com and writes an MLBlog, Tag's Lines. Follow @brianmctaggart on Twitter. Teddy Cahill is a reporter for MLB.com. Follow him on Twitter at @tedcahill. This story was not subject to the approval of Major League Baseball or its clubs.