It is a blow for the Whites, with a settled defence providing the bedrock for an unbeaten Championship run, which stretched to seven games before the international break.
And with fellow full-backs Marc Tierney (ankle) and Joe Riley (knee) still sidelined, and no joy in the loan market, Freedman could be forced to switch Alex Baptiste across from the left.
Tim Ream is the likely candidate to deputise on the left, leaving a space in the centre for either Zat Knight or David Wheater.
Freedman could, however, opt for a three-man central defence and operate wing-backs. Either way, he will hope McNaughton returns sooner rather than later.
“Kevin McNaughton has been jogging but still feels a little bit of pain in there so he is very doubtful,” said Freedman.
“It is a little more encouraging than we first thought, though.
“The full-back position is one place where we are short in the squad, particularly on the left.
“Unfortunately, I don’t think there is anything in the development squad or youth team that can bounce up and come straight in.
“We have to make sure we try to fill that position for the Christmas period and I am looking very hard.
“We can get away with a game here and a game there but over a six-game period we need to try and fill it and I am actively looking.”
Fellow defender Matt Mills admits the backline will miss McNaughton’s experience but believes they have able replacements ready to step into any reshaped back three or four.
Mills said: “Whenever we do defensive work in training, the manager is quite clever and switches it so we are always working with different partners on a day-to-day basis.
“So if there is an injury like Kevin’s, we are ready to make the change.
“It will be a blow because Kevin, like Loners in goal, has a lot of games under his belt and they bring a calming influence.”
Darren Pratley is back training and could travel but Craig Davies is expected to be absent with a slight hamstring problem.