Ian Burchnall has confirmed Richard Brindley will be out for the next six weeks after the Notts County defender suffered a fractured arm.
The former Rotherham defender picked up the injury in Saturday's 2-1 win at Dagenham as the Magpies secured a vital three points and he will require an operation.
The centre-back had to be replaced at half-time of the clash against the Daggers having only just returned to action from an Achilles problem.
Read more: Arter could transform Notts' promotion bid
Read more: Burchnall hails Arter impact after Forest move
It is a huge disappointment for both the club and the player who has been one of the most consistent performers in the heart of the defence this season.
Asked how much of a blow it was to lose Brindley at a key time of the season with Notts chasing promotion, head coach Burchnall said: "It's massive.
"I think he has been one of our most consistent players throughout the season no matter what the system or the shape that we've played.
"He kind of slots in different roles. He's been key in how we build-up play and bring the ball out of defence. It's a disappointing one. He was obviously working hard to come back from a small Achilles problem.
"He had a couple of games rest and we freshened him up. And then of course, and it's a little ironic that it's his arm that's injured. It's really bad luck.
"We've we've had a little bit of that with some of the defenders the past couple of weeks, but we're just working now to keep the others fit, working to try and get Kyle Cameron back and we'll just have to manage with it."
Brindley will now miss tomorrow night's clash against Boreham Wood at Meadow Lane which should allow Connell Rawlinson an extended run in the team.
The former Port Vale defender was excellent in Saturday's win at Dagenham and has now amassed more than 100 appearances for the club.
Rawlinson has had to be patient for his opportunity with Brindley and Kyle Cameron having forged an impressive partnership. Burchnall said he has proven to be a key part of the dressing room.
"When I first came in, we made some changes to the way that we wanted to play and try to move things in a slightly different direction," he said.
"Connell was somebody who really supported that and understood where we wanted to go and wanted to be a part of it. He was a driving force in the group and that's an important person to have around.
"He is somebody with a bit of leadership and cares greatly about the football club. You can see that he cares a lot about the club and its success. It's great for him to reach that milestone and hopefully a few more he'll get it'll get after that."
