The Rays designated Thompson (undisclosed) for assignment Wednesday, Tricia Whitaker of Bally Sports Sun reports.
Before he was optioned to Triple-A Durham on Aug. 2, Thompson had accrued a 6.11 ERA while striking out 12 batters over 17.2 innings in the big leagues this season. His results at Durham (3.26 ERA, 1.20 WHIP and 24 strikeouts in 19.1 innings) have been better, but he hasn't pitched for the affiliate since his demotion after being placed on the 7-day injured list Aug. 6. He'll likely stick around at Durham if he goes unclaimed upon being exposed to waivers.