Ollie Turton adds to Huddersfield Town injuries as defender is ruled out for three months by ankle ligament surgery
The defender needs surgery on problem, which he thought was innocuous at first.
"I've got some really bad news with Ollie," said Fotheringham. "He's got a really long-term injury.
"I had it at Norwich and was out for three months.
"He looks like he's going to need an operation as well. He's absolutely pushing himself to the limits and setting the standards every day. He's going to be a massive loss and it's really unfortunate news in that respect.
"But we all support him, he's a great boy with a lovely family to support him so I'm sure he'll be back in good shape in no time and I don't think he'll lose too much fitness as well because he's an athlete."
Turton picked up the problem in Saturday's 1-0 win over Millwall.
"He was quite shocked because he could put weight on the foot," said the coach.
"When he went down during the game we were all so shocked because he's not a player to go down in them moments. Even if he has an imapct injury he'll always get up.
"He's what I call a real Terrier, he just throws himself into tackles. He can get up and down for 90 minutes-plus.
"But it just opens up another opportunity for someone to come in."
Matty Pearson has recently had the screw removed from his broken foot but is still some way away from injury.
Fotheringham said the absence of the two experienced defenders will not affect the lcub's January plans.