General manager Jon Daniels said Harrison has been removed from all baseball activities. Harrison said a stiff neck turned into a stiff back on the right side.
He said he had more issues with the left side last year, which included surgeries in April and May to repair a herniated disk and nerve inflammation, forcing him to miss most of the season.
Harrison is scheduled to return to Dallas, probably this weekend, to see Dr. Drew Dossett, who did Harrison's back surgeries last year.
Harrison had neck stiffness Tuesday and was held out of a scheduled live batting practice session, even though he wanted to throw. He said he started feeling stiffness in his back Wednesday and was told the two aren't related.
"There's obviously some concern there from what happened last year," Harrison said. "I just hope that it's not a serious issue and 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."
The Rangers came into spring dealing with injuries to the rotation. Derek Holland, coming off a solid season with 213 innings pitched and a 3.42 ERA in 33 starts, is out until probably midseason after undergoing microfracture surgery on his knee in January.
"Hopefully this is irritation involved with getting going and he can push through it," Daniels said of Harrison. "After what he went through last year and the two surgeries, I feel for him.
"We're hoping for the best. With everything he went through last year, there is a level of concern. Hopefully, it's just some irritation from getting going."
Daniels noted that Harrison threw a lot this offseason and didn't have any issues, arriving in spring training ready to go.
The 28-year-old Harrison ended up having three surgeries last year, also undergoing thoracic outlet syndrome surgery later in the season. He went into 2013 looking to build off an 18-win season in 2012 and two straight consistently solid campaigns that earned him a five-year, $55 million deal, plus a club option for 2018.