Northampton Town midfielder Ian Morris will miss the rest of the season with a dislocated knee.
The 27-year-old suffered the problem on Monday and the day's training session had to be cancelled, such was the serious nature of the injury.
"I've never seen anything like that on a training ground. He twisted his knee in a real bad way," Wilder told BBC Radio Northampton.
The Cobblers will look to bring in two new players to cover injuries.
Darren Carter, also a central midfielder, is currently sidelined with a hamstring concern.
"I'd like to bring two in with Darren out for two to four weeks," Wilder said after Tuesday's 2-0 loss at Portsmouth.
"We feel for Ian. He's done really well for me since I've been here. Hopefully he will make a speed recovery.
"It was just a ball up in the air and he got his studs stuck in the ground and his full weight went right through his knee. It's a situation I've never experienced. It is something that couldn't be helped."