Wood has not pitched since July 11 because of the blister, and the Cubs thought the All-Star break would be enough time. However, he has yet to get in a game, and was not available Wednesday against Arizona.
"We thought the four days off at the All-Star break would be enough and he'd be ready to go in Houston," Cubs manager Lou Piniella said. "We were expecting that and so was Woody."
Wood was one of eight Cubs named to the National League All-Star team but was not available. Instead of being able to throw, he was limited to throwing changeups only on Wednesday at Chase Field in a brief side session.
"He's not capable of throwing a full bullpen where he throws his fastball, throws his slider," Piniella said. "I think that would send him totally backwards."
Wood, who has 24 saves in 29 opportunities, likely will need time to build up his arm.
"Not only do you have a little bit of a finger problem," Piniella said, "but the fact that he hasn't thrown the baseball in a long time, you have to get him on some kind of schedule once he's well to get his arm strength going."
Wood was not placed on the disabled list because the team expected him to be ready after the break. Carlos Marmol is the substitute closer until Wood is ready.
"It's a concern," Piniella said of Wood's injury. "The reason it's a concern is there's no timetable for this thing now. We felt four days off during the break, he'd get a nice throw day in Houston and he'd be ready to pitch. He hasn't been able to throw. Is it getting to be a concern? You're darn right it is.
"The skin hasn't grown back the way you'd expect it to grow," Piniella said. "They're going to check for a couple other things and then we'll know. We need the guy back, there's no question. Woody's just as concerned as we are. He wants to get out there pitching."
Outfielder Jim Edmonds also was not available Wednesday because he aggravated an old injury on his left knee and wasn't able to push off when hitting. He will undergo an MRI on Thursday in Chicago to make certain there's no tear.
"Outside of that," Piniella said, "we're fine."
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.