The bone chip was first 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 "non-issue," 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."