Wood gave up solo homers to Ken Griffey Jr. and two others, then left the game after only three innings because of more shoulder woes Wednesday night, leaving the Cubs with a much bleaker future following their 9-3 loss to the Cincinnati Reds.
"The last thing we need right now is for him to go down," catcher Michael Barrett said.
Wood (3-3) couldn't get loose on a warm, muggy night, an ominous development for a pitcher who has already tangled twice with shoulder problems this season. He was limited to three spring training starts because of bursitis, and was on the disabled list from May 3 to June 29 with a strained shoulder.
In his fifth start since returning, Wood never looked right.
"It's a concern, but you don't want to jump to conclusions yet," manager Dusty Baker said. "We took him out more as a precaution than anything. His velocity was down.
"He warmed up great and didn't feel anything. That one inning he started to feel something, whatever it was."
Wood was scheduled for an exam with Dr. Tim Kremchek on Thursday. The Cubs then will decide whether to get medical tests on Wood, who didn't stay around to talk to reporters.
Wood also left a game April 30 against Houston after three innings because of a sore shoulder, his prelude to going on the disabled list.
"It's kind of what he had in spring training and what we were dealing with after that Houston game," trainer Mark O'Neal said. "We don't want to let this develop into anything significant."
The Reds hit four homers in all, and Aaron Harang (6-8) pitched a seven-hitter for Cincinnati's first complete game of the season. Derrek Lee hit his major league-leading 31st and Jeromy Burnitz followed with a solo shot in the seventh, when Harang's shutout ended.
Cincinnati had gone a club-record 94 games without a complete game this season.
"Everything has to click to get a complete game," Harang said. "Your pitch count has to be low, the defense has to play behind you, and you need some runs early so you can relax even more. I was able to throw strikes and they were swinging at them."
The Cubs lost for only the second time in 10 games, a surge that moved them back into contention for the NL wild card. Wood's latest shoulder woes undercut the renewed optimism.
Wood gave up solo homers to Griffey, Felipe Lopez and Adam Dunn in three innings. An assistant trainer and pitching coach Larry Rothschild visited Wood after Griffey hit his 21st homer in the third inning, making sure he was all right.
Wood stayed in the game and retired the next two batters, but didn't return for the fourth.
"In the first inning, I thought he had pretty good stuff," Barrett said. "He just needed to get loose, get going. Power pitchers are like that. His last few starts he's been like that. Today he just had trouble getting loose."
The Cubs need Wood and Mark Prior -- who both have been on the disabled list this season -- to stay healthy if they hope to make a playoff run. Prior has recovered from a broken elbow, but Wood's shoulder remains a major concern.
With Wood not quite right, the Reds rolled out to a 6-0 lead. Griffey's homer was the first of his career off Wood and the 522nd of his career, breaking a tie for 14th on the career list with Ted Williams and Willie McCovey.
Javier Valentin, who homered from both sides of the plate on Sunday, added a solo shot as Cincinnati pulled away off the Cubs' bullpen. Griffey had an RBI single during a clinching three-run rally in the eighth.
The four homers moved the Reds back ahead of the Cubs for the NL lead with 125, one more than Chicago. More homers have been hit at Great American Ball Park this season than anyplace else in the majors.
Lee went 1-for-4 overall, dropping his average a point to .375, still the best in the majors. He is 17-for-34 (.500) with eight homers against the Reds this season, five of them at Great American.
- It was Harang's second career complete game in 77 starts. The other was Aug. 26 against St. Louis.
- Griffey has 1,508 RBI, one behind Mickey Mantle for 42nd on the career list.
- Barrett had a single and a sacrifice fly, extending his hitting streak to seven games.
- 2B Todd Walker's hitting streak ended at 12 games.
- Dunn has 25 homers this season, three of them off Wood.
- The Reds have given up 143 homers, most in the majors.
- RHP Greg Maddux needs six strikeouts on Thursday to become the 13th pitcher to reach 3,000.