Thanks Purni for your reply.
He do not remember any such agreements, and what my understanding is, if he had signed any such agreement, then the copy of the agreement should be provided. But there is no papers of such kind.
Yes, the company he is working now is existing client for the previous company. And he is not in sales or services in his previous company to add clients. He is an engineer, and he do not have any confidential business data or never worked on such assignments, just a good outstanding employee.
He left the organization and joined in the organization that is client of his previous company, my friend worked for this client sometime ago. It seems that the company wanted to add this person to same client for huge buks... but my friend got disturbed by then up with his company deeds as he was put on a crazy work and wanted to move out, company after tendiring resignation gave options but he lost faith and decided to quit.
Now the company is saying it is illegal to join their clients! and saying that it is according to NDA or agreement, which my friend do not have. He also spoke to his collegues and no one has the agreement copies with them ..