Ribeiro added: "Robinho said to Calderon that he was treating him the same as [FIFA president] Sepp Blatter claimed that Manchester United were doing with Ronaldo.
"That is, slavery. If they don't let Robinho go, he will continue, sad, and in the coming year will be worth far lower than the value currently offered by Chelsea."
Meanwhile, former Blues striker Adrian Mutu is expected to lodge an appeal after FIFA ordered him to pay the club £13.68million in compensation for testing positive for cocaine while at Stamford Bridge.
The Romanian international was sacked in 2004 after failing the drugs test and was banned from the game for seven months.
A Chelsea statement said: "This is an important decision for football. The original ruling recognised the responsibilities we all have in this area."