Zambrano had appeared fine until 15 minutes before the game, when he left the field during his warmup and left-handed reliever Sean Marshall headed to the bullpen to prepare for a spot-start even as Zambrano's name was being announced in the ballpark as the starting pitcher.
"He went out there to warm up, and he says after he threw two or three pitches that his back tightened up and he started getting spasms," manager Lou Piniella said after the game. "He's going to be sent home tomorrow and given a MRI. I guess we can go on those results."
Zambrano was already back at the hotel by the time the game ended, and the report Piniella got from the trainer was that "he's in discomfort."
Zambrano left his previous start after three innings with the same ailment, and though the move was meant to be precautionary, missing Friday's start is certain to raise eyebrows. When asked before the game if there was any concern about Zambrano's back, Piniella replied, "None at all," as the Cubs took batting practice Friday.
"We took him out of the ballgame in Miami last Saturday, and he only pitched three innings," Piniella said two hours before the game. "He hasn't complained about anything. He's been doing his exercises, getting his throwing in. So he should be nice and strong for tonight's performance."
The abrupt turn of fate was an understandable frustration to Piniella, who had to start the game out of the bullpen, with his long men, Marshall and Jeff Samardzija, throwing 62 and 73 pitches, respectively. Taxing the bullpen so early in a long series at a difficult park could force the Cubs' hand for immediate help on the pitching staff.
"He's done his [flat-ground] work," Piniella said. "He's thrown long. He took batting practice before the ballgame today. This is something that we found out 10 minutes before the ballgame started. If we had any prior knowledge, we could have pitched [Ryan] Dempster today. This would have been his fifth day. We didn't know."
Zambrano has made at least 30 starts every season since 2003 and has appeared on the disabled list three times, once in 2002 with a right elbow injury, once in '08 when he suffered a right shoulder strain, and earlier this season from May 4-22 with a left hamstring strain.
Zambrano had appeared comfortable and ready to pitch to all who saw him Friday. There was no concern that he may have been hiding discomfort during the week, and Piniella was surprised by the sudden shift in Zambrano's status.
"He was here early," Piniella said. "He hasn't gotten any treatment. He hasn't complained about anything. If he had complained about anything, obviously we wouldn't have scheduled him to pitch. I'm not going to pitch anybody with a bad back. If he were concerned, I don't think he would have taken BP. This is something that crept up on the spur. I didn't know anything about it until Larry came in here about six minutes to 7."
The Cubs are concerned about Zambrano's health and availability in the near future, but they also must focus on the next three days. The series in Colorado is a critical one for the Cubs, having lost the division lead to St. Louis, which won earlier Friday night, and falling two games behind the Rockies in the Wild Card standings.
Owen Perkins is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.