Overton discovered the extend of his injury after scans to diagnose the pain he felt in his chest after diving awkwardly to try to take a spectacular caught-and-bowled in the Perth Test.
He was then advised by England’s medics to be careful how he dived for the remainder of that match, which ended in an innings defeat for the tourists as Australia regained the Ashes in double-quick time.
Overton admits the temptation to try to recover for next week’s showpiece Boxing Day Test in Melbourne.
But with a potential recovery time of up to two months should the risk backfire and a final Ashes Test in Sydney as well as spring series in New Zealand to consider, the 23-year-old may have to sit and suffer.
“It’s a hairline fracture at the minute,” he said, before revealing possible repercussions of another blow in the same place.
“It could have made it worse, or punctured a lung or something.
“That’s why I was making sure I didn’t dive too much on it, because then it could break properly and you could probably puncture a lung.
“I was controlling the diving a little bit, trying to stay on my knees as much as possible.”
However, Overton admits that temptations do not come much bigger than the Boxing Day Test.
“The draw of playing in that game will be absolutely massive,” he added. “But I think you’ve also got to be realistic. There’s another game after Melbourne, and then the New Zealand Test series as well – so it’s the bigger picture, not just one game.
“There’s quite a lot of swelling in it, so we’ve been dealing with that.
“We’ll wait and see, but I hope three or four days will help.”
England may have to put their foot down for Overton’s own good – because he has been brought up to battle through whenever possible.
“I think as a young cricketer, a young sportsman, you’re always wanting to play games,” he said.
“Sometimes you have to be reined in a little bit, and told ‘Right, you’re not playing this game – it’s probably better for you to rest’.
“But I’m sort of wanting to play every game.
“It’s obviously quite sore but it just seemed like battling through the pain was in my nature,” he added. “I’ve always been taught to fight through things, and that’s what I’ve had to do this game.”