The 24-year-old right-hander (0-1, 7.71 ERA) left the mound in the first inning in Detroit on Thursday after appearing to suffer the injury during warm-ups. Sampson felt sudden discomfort in his elbow and had to be pulled from the game before throwing a single pitch.
Sampson said he had felt good during his pregame bullpen session, but he tired late in the warmup and began to feel like he couldn't finish his pitches. When he took the mound before the first inning in Detroit, his arm was sore and aching all of a sudden.
"My arm didn't feel good at all," he said. "I remember throwing that last pitch in warmups and, I think my arm was trying to protect itself, so I threw it and grimaced a little bit. I didn't feel it snap or pop or anything like that. I just felt total discomfort. I knew something was wrong. I was just listening to myself, which was tough. I'm right there on a big-league mound and I would have done anything to stay out but I just couldn't do it."
The injury requires surgery but it's not a tear of his ulnar collateral ligament, which would have required Tommy John surgery.
"It's the tendons that connect to the flexor and pronator, I believe. I'm not exactly sure though," Sampson said. "They're saying it's a Grade 3 (sprain), which is enough percentage (torn) where they have to repair it with surgery. I'm still in talks with the doctor and my agent and my family right now. Not exactly sure what the rehab process is but they're saying it should be good by spring training if anything."
Sampson made his major league debut five days earlier against the Boston Red Sox. Replacing an injured Wade Miley in the Mariners' rotation, Sampson allowed four runs and eight hits over 4 2/3 innings with a walk, two strikeouts and two home runs allowed.
"I haven't missed a start in my professional career and missing time and being here, being at the doorstep and feeling good about how my stuff is playing, it just sucks. There's nothing much else to say," Sampson said.
Information from the Associated Press was used in this report.