PFA Scotland and their lawyers believe the players are free agents under employment law but Green vowed to fight for transfer money and revealed he had written to every league club in the UK warning them to stay away from them.
Former Gers defender Steven Whittaker was unveiled as a Norwich player on Tuesday while Scotland Under-21 midfielder Jamie Ness has joined Stoke and forward Steven Naismith is expected to sign for Everton by the weekend.
All of those deals are free transfers after the players involved took up the right to not have their contracts moved over to the new company in charge of Rangers.
PFA Scotland are backing such moves and released a statement supporting them.
The statement read: "Whilst it is accepted that newco is entitled to argue breach of contract, the Players Union is dismayed that attempts are being made to prevent our members from playing professional football simply because they have exercised their legal right not to transfer to newco."