"He's uncomfortable right now," Rangers general manager Jon Daniels said Thursday morning. "He's thrown a lot this winter without any issues. Unfortunately, it's picked up again. After what he went through last year, there is a level of concern. Hopefully it's just some irritation he can push through, they can prescribe some medication and get him going."
Harrison, an 18-game winner in 2012, will undergo an MRI and scan on Thursday, then fly back to Texas to be examined by back specialist Dr. Drew Dossett.
Harrison said he wasn't happy that this was just now coming up after having no problems this winter, but it doesn't appear to be as serious as last season. Harrison said the issue is more on his right side than the left side, which was the problem area last year.
"I was 100 percent, and now I'm having some tightness there and I don't know," Harrison said. "I felt a little bit [Wednesday], and when I got up this morning, it was worse. I was ready to come in here and throw my live BP, it's just not happening."
"There's obviously some concern there from what happened last year. I just hope that it's not a serious issue, and [that it is just] something I can take a few days down and stay on top of my core program and get right back out there, and hopefully that's the case. But it's not fair to say that I'm not worried about it, because I've had a lot of issues recently."
Harrison made just two starts last season before being diagnosed with a herniated disk in his lower back. He underwent two operations -- one in late April and a second in early May -- and did not pitch the rest of the season. Dossett did the surgery both times.
"I'm not going to push through any pain if I'm having pain with it," Harrison said. "But I definitely need to keep my core strong, because it was up there. It was up to where it was supposed to be. And [I will] try to keep my arm going by doing some shoulder stuff in there, because I'm not able to throw right now."
The Rangers were hoping Harrison would be ready to go this spring and that he could regain his spot in the rotation. They already lost Derek Holland until midseason after he underwent microfracture surgery on his left knee.
The Rangers' rotation right now includes Yu Darvish, Martin Perez and Alexi Ogando. Harrison was supposed to be in there as well. The Rangers' depth includes Colby Lewis, Robbie Ross, Tommy Hanson and Nick Tepesch, who are all trying to compete for a spot.