The Mariners were off Monday, so a roster move to fill Pryor's spot on the 25-man roster won't be announced until prior to Tuesday's 7:10 p.m. PT game against the Tigers.
Pryor pitched in seven of the Mariners' first 14 games this season and had not allowed a run in 7 1/3 innings. The hard-throwing youngster allowed just three hits and one walk, while striking out seven.
Pryor appeared in 26 games last year for Seattle after a midseason promotion, posting a 3-1 record and 3.91 ERA in 23 innings.
The Mariners could recall Lucas Luetge, who was just sent down to Triple-A Tacoma last week, though that would give the bullpen four left-handers. Available right-handed relievers in Tacoma include Logan Bawcom, Danny Farquhar, Jhonny Nunez, Brian Sweeney and Yoervis Medina.
Of that group, only Medina is on the 40-man roster, so any other promotion would require a move to create a spot.
Veteran right-hander Kameron Loe was claimed off waivers by the Cubs on Saturday after being designated for assignment last week by the Mariners. Josh Kinney, another veteran right-hander, is on the 60-day disabled list with a stress reaction in his ribs.
Hector Noesi, who has worked some in relief in the past for both the Yankees and Mariners, was just promoted to Tacoma from Double-A Jackson on Monday after pitching 11 scoreless innings with five hits, three walks and 12 strikeouts in his first two starts with Double-A Jackson.
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB as well as his Mariners Musings blog. This story was not subject to the approval of Major League Baseball or its clubs.