Tampa Bay designated Muller for assignment Sunday.
Muller will cede his spot on the 40-man roster to lefty Joe LaSorsa, whose contract was selected from Triple-A Durham prior to the Rays' game Sunday versus the Dodgers. Though he was up with the big club for a brief spell earlier in May, Muller never made his MLB debut before he was sent back to Durham just under two weeks ago. In 16 appearances out of the Durham bullpen this season, Muller has logged a 4.95 ERA and 1.50 WHIP across 20 innings.