Sampson was supposed to receive two cortisone shots Tuesday, but he battled migraines all day and was vomiting. He was feeling much better upon his arrival at the ballpark Wednesday, but said he'll need three to five days for the cortisone to work to its full extent.
"I've got to rest it, and let the inflammation get out of there and let the cortisone take over and get to work and stay positive and rest it," Sampson said. "Hopefully we can get back to where we were."
Sampson posted a 1.50 ERA in his first 19 games of the season, but he had allowed 12 hits and 11 earned runs in two innings in his next three outings while battling the shoulder injury.
"It had quite a bit to do with it," Sampson said. "It wasn't letting me finish pitches. No matter how hard I tried to battle through it, it was affecting me. I had to get something done and see exactly what it was and what was causing it, and thank goodness we found it and got the cortisone and we can get back to where we were."
Sampson, who was on the disabled list last year with right shoulder spasms, said he learned from former teammate Doug Brocail last year to not pitch through pain.
"It's hard because we're all competitors, and we all want to take the ball, but it was getting to the point [where] I wasn't doing myself or the team any favors," Sampson said. "I decided to speak up and try to get it better."