The team is returning Harrison back to Texas from spring training in Surprise, Ariz. to undergo an MRI, after he threw a full bullpen session on Sunday.
Harrison only made two starts last season, losing both games, before suffering a herniated disk in his lower back. He had surgery twice and ended up missing the rest of the season.
He went 18-11 with a 3.29 ERA in 32 starts in 2012.
"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."
"He's uncomfortable right now," Rangers general manager Jon Daniels said. "He's thrown a lot this winter without any issues. Unfortunately, it's picked up again. Hopefully it's just some irritation he can push through, they can prescribe some medication and get him going."