Kela was placed on the DL in April after having surgery to remove a bone spur in his right elbow. He made four rehab relief appearances for Triple-A Round Rock and Double-A Frisco, throwing four shutout innings with seven strikeouts and zero walks. He had a 7.11 ERA in seven games for the Rangers before going on the DL.
Diekman, who is 1-1 with a 2.73 ERA in 39 relief appearances, is eligible to return from the DL on Thursday.
Cash Kruth is a reporter for MLB.com. Follow him on Twitter at @cashkruth. This story was not subject to the approval of Major League Baseball or its clubs.