They need to give him his unconditional release from his contract and let him go to whatever team is willing to pay him the most. They have the right to set conditions for his employment, but not to keep him like an indentured servant. Seems to me they have breeched their contract with him. Let the courts decide if they want to go that route.
They don’t need to do any of that. He has made himself unavailable to the team. They haven’t breeched anything. He is functionally sitting out. This is what happens when you sit out.