Already recovering from shoulder surgery and a knee injury, Lilly missed most of this week with a 103-degree fever and flulike symptoms.
"I haven't been on my feet much at all in the last five days," the left-hander said Friday, when he returned to camp and did some light throwing. "I was in bed for 18 hours a day."
Manager Lou Piniella and GM Jim Hendry had been saying Lilly would miss the season's first few weeks. Lilly had hoped to prove them wrong, insisting he could be ready by opening day, but he now realizes that's unlikely.
"I'm just going to get back as soon as I can. I don't know what that day is going to be," he said. "I don't want to start the season on the disabled list. I don't feel good about that. I don't like being on that list or associated with it in any way, shape or form."
Lilly, the team's lone All-Star last season, went on the DL last July with shoulder inflammation and had arthroscopic surgery on his left knee while he was out. He returned to pitch the final six weeks and finished 12-9 with a career-best 3.10 ERA.
He had arthroscopic shoulder surgery Nov. 3. He repeatedly said he was progressing well, but he was set back when he hurt his right knee early in camp. At the time, he said he might have been favoring his left knee.
Then came his illness. Lilly said his wife, Natasha, who is eight months pregnant with their first child, nursed him back to health.
"Flu. Body aches. Head. Stomach. A little bit of everything," he said. "Just standing feels good, being on my feet, being out of bed. It makes you really appreciate your health when it's taken away.
"We'll work to get back as soon as possible. I would have liked to have been (ready for opening day), but even just five days makes it tough. Being out is going to cost me more than that."
Lilly, who signed a four-year, $40 million contract before the 2007 season, has a 40-26 record and 3.70 ERA with the Cubs. He and two big-money teammates, Derrek Lee and Aramis Ramirez, could become free agents after this season.
Though the Cubs still are trying to fill the rotation spot vacated by Rich Harden, who wasn't re-signed after 2009, Piniella said he won't rush Lilly.
"We're going to take it easy with him," Piniella said. "When we get him on the mound, it's because he's ready to go. He's a hard worker, so we'll get him going in the program he was on."
"We'll have a nice offense," Piniella said. "We've got some work to do with our pitching, though, we really do."
NOTE: With veterans Kevin Millar and Chad Tracy available to strengthen the bench, Piniella said he probably won't have to use pitcher Carlos Zambrano as a pinch-hitter this season. Zambrano, who holds the team record for pitchers with 20 home runs, went 1 for 7 as a pinch-hitter last season.