Hultzen will undergo treatment over the next few days and plans to begin playing catch again on Tuesday.
"I'm not worried about it at all," he said. "I'll be back out maybe tomorrow to throw a little bit to see how it feels. It's not a sharp pain, but it does inhibit the way I run and throw."
The injury first occured Saturday during conditioning drills, then got worse through additional workouts until the lefty told staff members what he was feeling.
"Nothing felt bad instantly, it didn't pop or anything like that, but after we ran, it started to feel sore and it got worse and worse," he said. "I tried to run yesterday, and it didn't feel good. Then I felt it while I was throwing a little bit, so I just went and said I felt a little tight. We did some tests then and found there was something."
Once Hultzen is back to participating in normal baseball activies, he will throw a bullpen session. After that, however, the schedule is unknown.
Hultzen originally thought about pitching through the discomfort, but this early in camp, he decided not to take any chances.
"It's tough to tell someone you're feeling something, but it's the smart thing to do; get it treated, rest a little bit and get back at it in a few days," he said. "I've seen guys try to toughen up and work their way through and only end up making it worse. I didn't want to be that guy."
Hultzen, the club's No. 2 prospect according to MLB.com, has pitched three scoreless innings this spring, striking out six batters and allowing just one hit.
Last season with Double-A Jackson and Triple-A Tacoma, Hultzen combined for a 3.05 ERA over 124 innings while striking out 136 batters.