The 21-year-old, on loan from Burnley, has been ruled out for around six weeks due to an ankle ligaments injury picked up in training.
Hearts boss Craig Levein confirmed the blow ahead of Sunday’s 2-1 defeat to Rangers with the returning Christophe Berra partnering Michael Smith in the centre of defence.
He said: “We had him (Jimmy Dunne) scanned and unfortunately it looks like he is out for six weeks or so.
“It’s a training injury and it’s one of those things. It’s ankle ligaments.
“I was looking forward to getting Christophe (Berra) back to pair him alongside Jimmy (Dunne) at some point but obviously that’s not going to happen.”
Dunne confirmed on Twitter that he has returned to parent-club Burnley for treatment with his loan deal set to expire in January.
However, he could be back at Tynecastle with a deal agreed in principle with the Clarets for the loan to be extended until the end of the season.
The Irishman tweeted: “Injuries are a part of football, currently getting my treatment back at Burnley but eager to get back out there as soon as possible! Thanks for the support Jambos fans.”
Join our Facebook group Our Edinburgh to share images and news from and around the Capital