The Professional Footballers' Association has said it will "robustly defend" Richard Keogh after his dismissal by Nottingham Forest's arch-rivals Derby County last week, the BBC has reported.
Keogh had his contract terminated with immediate effect for "gross misconduct".
The Republic of Ireland international defender faces at least a year out after he suffered a serious knee injury in a car crash that resulted in Rams team-mates Tom Lawrence and Mason Bennett being convicted for drink-driving.
Lawrence and Bennett were both disqualified from driving for two years, given a 12-month community order each and ordered to carry out 180 hours of unpaid work.
They were also both fined six weeks' wages by the Rams and told to serve an additional 80 hours of community work and rehabilitation, which includes a drink aware course.
Keogh's contract was due to expire in 2021.
It is understood Derby offered the 33-year-old a revised deal on reduced wages.
He had 14 days to appeal the club's decision to terminate his contract and the PFA has said it will back him.
"We will robustly defend our member because we feel he has been unfairly treated," said a PFA spokesman.
Derby have said they will not comment further until the outcome of any appeal.
