The Professional Footballers' Association (PFA) will "robustly defend" Richard Keogh after his sacking by Derby County.
Keogh was sacked over his involvement in a car crash which saw team-mates Tom Lawrence and Mason Bennett arrested.
Lawrence and Bennett were both fined six weeks' wages by the Rams and pleaded guilty to drink driving.
"We will robustly defend our member because we feel he has been unfairly treated," said a PFA spokesman.
Keogh, 33, suffered a knee injury in the crash on 24 September and will be out for around 15 months. His contract was due to expire in 2021.
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It is understood Derby offered Keogh a revised deal on reduced wages.
The player will appeal against Derby's decision and the PFA have told him they will back him in that and any subsequent challenge to his dismissal because they do not view the treatment of Keogh as being in line with the action taken against Lawrence and Bennett.
In announcing Keogh's dismissal, Derby said they would not comment further until the outcome of any appeal was known.