Eyre strained his left groin on Thursday, and was to spend Friday on the stationary bike and with an ice bag nearby.
"All day long, I get to ice -- it's not the greatest area to ice, by the way," Eyre said of his plan for Friday.
"I threw it and went, 'Oh, that didn't feel so good,'" Eyre said. "I tried to stretch it on the mound. I tried to throw a fastball, and it kind of hurt a little bit, and that's when I bent over on the mound and tried to stretch. That's when they came out to the mound. I said, 'I'm fine, let's go.' That's when the tough guy in you takes over. It was already 11-0."
Eyre walked Markakis and gave up a single to Kevin Millar before he was lifted. His leg was wrapped all night, which wasn't too comfortable, he said.
"They don't want to do the DL yet," he said.
Teammates have told him not to push it.
"Not to be a tough guy, but it's hard for me not to push it," Eyre said. "I've been throwing the ball well and feeling good. You want to help this team win games. But winning games in June isn't as good as winning games in August and September."
The Cubs will enter the three-game rematch against the White Sox with one lefty, Neal Cotts, in the bullpen. Neither lefty pitched in the three Interleague games against the White Sox at Wrigley Field last weekend.
"Let's hope they don't need us this time," Eyre said.
The Cubs have had a rash of injuries lately, but if Carlos Zambrano's bullpen session Sunday goes well, he could start next Friday in St. Louis. Outfielder Reed Johnson may be activated on Thursday.
"We've been dealing with it for a little bit now," Cubs manager Lou Piniella said of the injuries. "So far, we've been able to maintain. Hopefully, we'll continue to. We've [shown] resiliency. I expect us to play well but, at the same time, we can't afford too many more of these things."
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.