Wood, who had been healthy all spring, hasn't pitched in a Cactus League game since Sunday. Manager Dale Sveum mentioned Saturday that Wood had a slight back issue that previously had been unknown.
"(Wood is OK) besides the back, but other than that he's been fine," Sveum said. "The back always flares up once in a while but it's not a concern now. It's fine."
Wood was on the disabled list at the start of the 2010 season with a back injury while playing for the Cleveland Indians. He missed a little more than a month. That back problem also surfaced in spring training.
Three of Wood's four outings this spring have been scoreless. He faced the Chicago White Sox Sunday, giving up two hits but not allowing a run.
Sveum suggested that Wood could be used in games toward the latter portion of the Cactus League schedule. Including Saturday, there are 11 days of games remaining.
"There's no issue, it's just mainly backing him off and getting him a couple more outings before the season starts," Sveum said. "It's just rest or whatever. He got his work in and it's now back off a little bit and get him a couple of innings before the season starts."
Meanwhile, an MRI on Mateo's right elbow showed no structural or ligament damage.
Mateo said Saturday morning that the MRI results are similar to ones he had last year -- and that injury cost him nearly three months of the season. He will be shut down for 10 days, then be re-examined by the Cubs' medical staff.
"Opening Day is obviously out of the question for him now," Sveum said.
On July 4, Mateo left a game and was eventually diagnosed with right elbow soreness. He never pitched again in 2011.
It's a tough blow for a club that is looking for relievers to step up this spring. General manager Jed Hoyer has called the bullpen the area where the team has the most decisions to make. Jeff Samardzija's move to the rotation adds yet another vacancy to fill.