Cash said it's definitely possible that Whitley will be with the Rays in September, when rosters expand to 40 players.
Whitley had a 0.86 ERA in 21 rehab innings. He hasn't pitched in the Majors since May 2015, after undergoing surgery to repair a torn UCL. He makes his home near Montgomery, Ala.
"He's part of our big picture and part of our plans moving forward," Cash said. "Without a doubt."
• Rays starter Alex Cobb threw four innings in his rehab start for Triple-A Durham on Tuesday and allowed one run. Cash said all the reports on Cobb were positive.
The right-hander will be back in St. Petersburg by Thursday to throw a bullpen session before going back out on his rehab assignment. Cobb is also recovering from Tommy John surgery, and he hasn't pitched in the big leagues since 2014.
Sam Blum is a reporter for MLB.com based in Tampa. This story was not subject to the approval of Major League Baseball or its clubs.