Diekman finalized a one-year contract with the Rays on Wednesday.
Tampa Bay designated right-hander Chase Anderson for assignment to clear a spot on the 40-man roster and 26-man active roster for Diekman. The 36-year-old will provide the Rays with another left-handed relief option in the wake of Garrett Cleavinger's (knee) season-ending injury. Diekman had posted a 7.94 ERA and 2.12 WHIP in 11.1 innings with the White Sox before being released over the weekend.