The bone chip was discovered during a 2014 MRI before the left-hander signed his six-year deal with the Cubs, according to Yahoo! Sports, which is including the information in an upcoming book.
Lester calls the chip a "nonissue," according to the Chicago Sun-Times. Lester pitched 205 innings in the regular season last year, plus another 14 in the postseason. If the chip moves, however, Lester acknowledges that he may have to address it with surgery.
"It's just a matter of hopefully it stays put, and we don't have any worry about it," Lester said, according to the newspaper. "And then if it does become a concern, if I start having inflammation or missing starts because of it, then that's when we'll probably sit down and talk to somebody about getting it removed. As of now, knock on wood, I haven't had any concern with it."
The Cubs did their homework before signing Lester.
"We did a very thorough exam including imaging of the shoulder and elbow," team president Theo Epstein said Friday, according to the Sun-Times. "We were really quite pleased with the results, as Jon compared very favorably with most of the free agent pitchers we have examined and MRI'd over many years.
"Virtually all pitchers have some wear and tear on their shoulders and elbows, and Jon's imperfections were very manageable. He remains very consistent, as we hoped, throwing 200-plus quality innings yet again last season."
Lester didn't advertise that he had a bone chip as he was being courted as a free agent in 2014, but the Cubs were willing to take the risk. And as long as it isn't bothering him, Lester has no plan to address it.
"It's kind of one of those deals if it's not bothering you, don't mess with it," Lester said, according to the Sun-Times. "You start getting cut on and doing rehab, and that's when maybe they're in there, taking that bone chip out, and it puts more stress on something else. You don't know. 'If it ain't broke don't fix it' type thing."
Cubs manager Joe Maddon didn't even know about the bone chip, but when informed, he had only praise for Lester.
"I've watched him throw in this camp and think he's throwing the ball as well as I've ever seen him," he said. "His delivery is as good as I've seen him. His arm stroke is beautiful."
Maddon took a practical approach to the situation.
"A bone chip is a bone chip. Just go play and if there is an issue with it you go attack the issue and move on forward from that," he said.
Lester, speaking more about the bone chip after the Cubs' spring training game Sunday, said it was a relatively small problem.
"You can take any pitcher in this game and stick him in a tube you're going to find something," Lester said.
"I've dealt with bigger things throughout my career. I haven't missed any time with elbow problems," Lester said. "I know for a fact it's been there for a while."
Lester added that "if it was a serious issue the contract I signed wouldn't be what it is."
"I finally read the chapter the other day. Theo hit the nail on the head knowing me and my strength program," Lester said of the deal he signed with the Cubs. "And what I do to maintain a healthy body and healthy arm. To be honest I don't think I would have failed a physical but I think that was the ease of mine from Theo. Knowing where I came from and what I've been through and the work I've put in."
Information from ESPN's Jesse Rogers was used in this report.