A report in the Herald Sun on Tuesday said the midfield star, who relinquished the Blues captaincy for this season to concentrate on his own performance, had delayed talks on a new contract until at least mid-season.
The report said Judd, 29, might consider an early retirement to pursue other interests.
Kernahan admitted he was unsure how much longer the dual Brownlow medallist would extend his brilliant 239-game career.
"Put this on the record: he is 29 and I reckon he's got years to go," Kernahan told the Herald Sun.
"Will he last as long as we hope he does? I have a feeling maybe not.
"He's got some serious football left in him, and that's my personal opinion.
"But he might surprise us.
"I have heard the things where he might only have a couple of years left.
"You hear all the stories, but Judd will know himself.
"He has been around the coalface for all his career, and he obviously made the call along those lines to release the captaincy, and give someone else the chance.
"He has had to do a hell of a lot at our club in the last five years but, if it's typical Juddy, he won't change at all."
