The Latics announced on Monday that they had dismissed the 22-year-old former West Ham trainee following his arrest by the National Crime Agency (NCA) as part of its probe on spot-fixing in football.
The NCA, which was acting on information passed to it by a newspaper report, last week bailed Montano and five other players until April without bringing any charges against them.
Oldham had originally suspended Montano but made the decision to sack him following their own investigation, citing "gross misconduct".
However, Montano has hit back at the club for axing him and not listening to his protestations of innocence.
A statement issued by barrister Roy Ledgister, representing Montano, said: "Following his arrest for spot-fixing, Cristian Montano is disappointed to have learned of Oldham Football Club's decision to terminate his employment contract.
"Despite reports to the contrary, he had been suspended on full pay to enable the club to investigate. He will now mount an appeal challenging the club's recently and unexpectedly announced decision to terminate (his contract), which seemed illogical as it appears no proper investigation was carried out.
"Moreover a police/criminal investigation is ongoing without charges having been brought. The club would usually have interviewed their player as part of their investigation, instead they chose to engage in 'lengthy discussions' with their lawyers.
"Cristian has at all times been available to speak with them and naturally, as is his right, would have liked to have made sure that the club and its fans understood his denial of wrongdoing. It appears, however, that he has been pre-judged by the club on the inconclusive material presently available.
"He vehemently denies being involved in spot-fixing and welcomes the criminal investigation, with which he will fully co-operate."
Oldham had claimed Montano's conduct had breached club discipline, while insisting the move to sack him would not prejudice the NCA's legal case.
In their statement on Monday, issued on their website through CM Solicitors, they said: "After a thorough investigation carried out by Oldham Athletic Football Club relating to the conduct of Cristian Montano and following lengthy discussions with our team of legal advisers at CM Solicitors, a decision has been made by the club board to dismiss the player forthwith.
"Notwithstanding and without prejudice to the ongoing criminal investigation, it is our view that the player's conduct, in not only bringing the name of Oldham Athletic but also the football authorities into disrepute, amounts to very serious breaches of club discipline and therefore constitutes gross misconduct.
"Oldham Athletic take matters such as this extremely seriously and believe it was essential to act as swiftly as possible in conjunction with our legal advisers to investigate and deal with this matter decisively once they became aware of the allegations and irrespective of any other investigations and proceedings by other agencies."
Source: PA
Source: PA