The Rangers boss said: "Filip won't be seen again until after the winter break. It's a foot issue. I'm not a doctor but I'm told it's a unique injury.
"The doctor told me that in his 25-year experience in medicine, he had only seen this issue on a couple of occasions. It's a difficult one to put an exact date on the time he will be out.
"But he is going to be in a boot for four to six weeks. That's the starter pack so let's go from there and see how it progresses.
"I think he's been in the boot for a couple of weeks now so he will be in a boot until after Christmas and then it will be a case of building the fitness back up and whether there is a reaction from the injury because it's quite a rare one."
Gerrard, meanwhile, has confirmed Rangers' squad is poised for a January cull.
Matt Polster, Jamie Murphy and Greg Docherty are set to be made available and loanee Andy King is likely to be sent back to Leicester City.
Glenn Middleton, due to return from a loan at Friday's opponents Hibs, could be farmed out again.
Gerrard said: "There will be people leaving the football club in the window but I respect my players and won't name any individuals for now.
"You have to be honest with players and respect them. Unfortunately, we can only pick an 18 man squad."
Gerrard will be without top-scorer Alfredo Morelos after his Fir Park dismissal and the Ibrox boss revealed the striker had made his frustrations clear.
He said: "I think Alfredo has apologised to his team-mates after the Motherwell situation, but that's not important now.
"We have to focus on what's available to us. Alfredo has been different. You can see in his face he's disappointed not to be available. He's not a man who hides that disappointment very well.
"You can see even in today's session that he's gutted."
https://www.dailyrecord.co.uk/sport/football/football-news/filip-helander-blow-rangers-steven-21128287