Forced to sign a settlement waiver, can we still sue?

Dear Friends

This is very important

My client has been cheated by a real estate company and now they owe him a large sum of money. However, before giving his payment, they are asking him to sign an undertaking that he has received full and final settlement and that he wouldnt sue them in court.

At this stage, he dont have any option but to sign the undertaking. But after receiving his payment, can he go to the consumer court and claim the damages and remaining payment.

 Will the court accept his plea though he has signed the full settlment undertaking.

Pl advise?