Joe Savery was optioned to Triple-A Lehigh Valley, leaving Antonio Bastardo as the only lefty in the bullpen.
Contreras is viewed as a back-of-the-bullpen reliever, but he hasn't pitched in the big leagues in almost a year, so the plan is to bring him back slowly.
"Right now I'll stick with [Chad] Qualls a little while if that's possible. We'll give Contreras a couple of outings where he can get in some work at the big league level," manager Charlie Manuel said.
Contreras completed a rehab assignment with Class A Clearwater by pitching back to back on Thursday and Friday, as he pronounced himself ready to go.
"I feel good," Contreras said. "I'm very happy to be back, because my health is good and my arm is good and I can help the team."
Paul Hagen is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.