Pimentel was claimed off waivers from the Pirates on April 11 and was 0-1 with a 3.97 ERA in eight games for the Rangers. They have 10 days to trade, release or outright him to the Minor Leagues.
More bullpen moves are expected later this week. Reliever Kyuji Fujikawa's 30-day medical rehabilitation assignment ended on Wednesday and he re-joined the Rangers. He could be activated as early as Thursday. He had a 3.86 ERA in 10 games for Round Rock.
The Rangers may also be close to bringing Tanner Scheppers back from Round Rock. He has not allowed a run since being sent down on April 27 to work primarily on his fastball command.