Pryor initially tore the latissimus dorsi muscle in his right shoulder off the bone, then spent three months doing rehab as the injury healed. But the reattached tendon retracted during his recovery and attached to his triceps muscle, which is why he started having issues with his triceps when he started throwing again.
An MRI test revealed the new problem. Doctors removed the tendon from the triceps and attached it in the proper place using a technique first introduced on veteran pitcher Jake Peavy when he was with the White Sox in July 2010.
Peavy missed six months and had a difficult 2011 season before becoming an All-Star in '12. He is still pitching, now with the Red Sox. Pryor and a Minor League hurler are the only pitchers who have had the same surgery since, so this is somewhat new medical ground.
That is why Pryor and the Mariners are being vague on a potential return date, despite the youngster's apparent optimism.
"I mean, I really don't know," Pryor said. "It was just kind of a freak thing. I'm the second Major Leaguer to have this surgery and come back from it, so it's kind of unknown territory. [Peavy] had a complete tear, where I had a partial tear. So there's not really a timetable on it. I'm feeling good, but I think it'd be a stretch to be ready by Opening Day obviously. But hopefully not far beyond that would be a good goal."
The hard-throwing right-hander was a big part of Seattle's bullpen plans a year ago and he threw 7 1/3 scoreless innings in seven appearances before hurting his shoulder in mid-April.
Pryor has been playing catch at 110 feet and doing some light throwing in pickoff and fielding drills, but the real test won't come until he gets on a mound and fires with full force off the incline. The Mariners proceed carefully before giving him the green light to return and he figures he'll need eventually to prove he can throw hard on back-to-back days several times before getting a chance in games.
But whether that potential return comes a month or two, or longer, into the season, the Tennessee native is intent on regaining a role on the team that drafted him the fifth round in 2010.
"I want to pick up where I left off last year," said Pryor, who has a 3-1 record and 2.97 ERA in 33 appearances since being promoted in the middle of the 2012 season. "I felt like early in the season I earned a spot in the 'pen and was able to come in in pressure situations and later in games. I'd like to have that role again. I know it's something I've got to earn, with a new coaching staff, coming off an injury. So time will tell."