Murphy hit a combined .222 with three home runs and five RBIs on a seven-game rehab assignment with Class A Stockton and Triple-A Sacramento after being placed on the DL with right elbow inflammation on May 19.
He was batting .147 during his last 17 games with the A's after hitting .286 over his first nine contests while splitting time between second and third base. He is expected to get a few innings under his belt during the next week with Interleague Play in full bloom.
"Everyone knows they have a chance to get in the lineup," Geren said. "When you're playing a National League team, you could go through a whole roster."
Petit had been recalled from Sacramento on May 16 and made his Major League debut two days later, getting playing time when an injured Mark Ellis was out of the lineup. The 23-year-old, who hit .333 in 10 games with Oakland, admitted last week he might be served better with the River Cats seeing more action.
"He'll be able to get more experience down there," Geren said. "We want to keep his versatility up."
Jane Lee is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.