Contreras completed his rehab from last June's Tommy John surgery with another scoreless inning in Triple-A Indianapolis' Tuesday morning game.
"We're thinking of bringing him back Friday for the opener of the series with Washington," manager Clint Hurdle said. "If he feels well [Wednesday], that's what we anticipate."
Activating Contreras will probably again shorten the stay of Bryan Morris, who was called up Tuesday in place of Jonathan Sanchez when the left-hander was designated for assignment.
In a total of six relief appearances while working his way up the Pirates' Minor League chain, Contreras logged seven innings and allowed three runs, walking one and striking out eight.
Contreras, a 41-year-old Cuban right-hander, will be resuming a Major League career consisting of 292 appearances, the last 101 in relief for the 2010-12 Phillies.
Tom Singer is a reporter for MLB.com and writes an MLBlog Change for a Nickel. He can also be found on Twitter @Tom_Singer. This story was not subject to the approval of Major League Baseball or its clubs.