The Mariners designated Mastrobuoni for assignment Friday.
Mastrobuoni went 5-for-23 with an RBI and three runs scored during his eight-game stint with the Mariners, but he'll now lose his place on the 26-man and 40-man rosters in favor of Weston Wilson. Mastrobuoni owns just a .567 OPS across 474 plate appearances in his MLB career, but his defensive versatility could draw some attention on the waiver wire.