Cole, who went on the DL on July 9 with a sore latissimus, has two possible re-entry points: Either Wednesday night's series finale against Atlanta at PNC Park, which would come on regular four days' rest, or Friday's opener of a weekend series in Milwaukee.
"We anticipate we'll activate him when we determine when he will pitch the next time," Hurdle said. "[Friday's rehab start] went very well. He passed all the tests."
Cole went seven shutout innings on 92 pitches in Friday's wrap of his odd four-start rehab assignment.
In starts Nos. 1,3,4 -- all with the Triple-A Indians -- he threw a total of 18 shutout innings, yielding 11 hits; in start No. 2, he was rocked for five runs and 10 hits in 4 1/3 innings.
Pittsburgh's current probable starters for Wednesday and Friday are Charlie Morton and Jeff Locke, respectively. The rest of the current rotation consists of Francisco Liriano, Edinson Volquez and Vance Worley.
Whether the starter who relinquishes his spot to Cole gets recast in the bullpen "depends on who that guy will be," Hurdle said.
"We're still having multiple conversations," Hurdle added. "The guys we're talking about, I don't think, any of them have pitched in the bullpen with any regularity."
That doesn't eliminate anybody: All five current starters have predominantly started throughout their pro careers, Minor League phases included. The only one with significant relief experience is Morton, in the lower Minors with his original organization, Atlanta.
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.