The Reds, who are in the middle of a poor Championship run, have been rocked by further defensive injuries.
Hefele has played 18 games for the Reds this season, but has not featured since picking up an Achilles injury in the 4-2 win over Leeds United on New Year's Day.
Speaking to the press ahead of Saturday's Championship game against Wigan Athletic at the City Ground, manager Martin O'Neill broke the bad news about the 28-year-old.
Admitting Hefele is going to need surgery, the Forest boss told BBC Sport. "I am not likely to see him this season. It may be early to make that prognosis but I don't expect to see him."
In addition, Dawson is expected to miss six weeks after returning to training last week following a hamstring injury, but suffering another setback during O'Neill's first training session.
Here is how some Forest fans reacted to the sad news on Twitter:
This season is a write off. Gone from close to the top 2 to mid table in a month— Mark Shaw (@MarkShaw_Design) January 24, 2019
Hefele like Dias has proven to be a inspirational singing from karanka— martyn (@martynbigdog) January 24, 2019
That's what happens when you buy injury prone players simple as. Not good enough— Jonathan Antcliffe (@Jonny90nffc) January 24, 2019
— Chris (@88RedC) January 25, 2019
What a write off this season has turned out to be. Send Hefele back to Huddersfield. Complete waste of time
I know every club has it's injury problems and clubs that don't - like Burnley the season they went up - have a much better chance of achieving promotion. But come on Forest! Surely it's not normal the injuries our players have had over the last few years!— Owain Parry (@owskie81) January 25, 2019
Stop buying biscuits pic.twitter.com/BKuuiVdRtO
Wtf happened to him— Rich Hall ✌ (@Rich_T_Hall) January 24, 2019
O’Neill will be hoping to secure his first three points as Forest manager after a 1-0 defeat to promotion rivals Bristol City in his debut game last time out.
The Tricky Trees currently sit 12th in the Championship table after winning just one of their last eight games, a run during which the club parted company with Aitor Karanka.
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