Jensen was designated for assignment by the Mariners on Wednesday.
Seattle had to free up a 40-man roster spot after acquiring both Seby Zavala and Carlos Vargas from the Diamondbacks on Wednesday in exchange for Eugenio Suarez. Jensen, 25, struggled to a 5.32 ERA and 1.82 WHIP in 64.1 innings of work this past year between Double-A and Triple-A. He's yet to appear in a major-league game.