Dembele is approaching the end of his contract at Barcelona and his looming free agent status has seen a host of top sides, including Premier League pair Tottenham and Newcastle, keen on securing his services.
Barcelona have so far failed to convince Dembele to sign a new contract and believe the player is asking for too much money.
They are prepared to make the Frenchman sit in the stands for the remaining months of his contract if he does not sign, but Sissoko has struck a combative note.
The agent insists that money is not his client’s driving force, while biting back at Barcelona for suggesting they will not play him if he does not sign.
“It is pressure that does not work with people like us”, Sissoko told French radio station RMC about the sit in the stands indication from Barcelona.
“Maybe it can work with agents who are FC Barcelona cronies, but that is not my case, I am here to defend the interests of my player.”
He added: “Yes, we have demanding demands, but we have already shown that Ousmane’s career choices were not dictated by the money, otherwise he would not be here.
“Then if Barcelona wanted to negotiate, they could have come to the table with us to discuss.
“Except that there is no discussion and threats of no longer playing on their side. That is forbidden. We will assert Ousmane Dembele’s rights if necessary.”
It has been indicated that Barcelona believe Dembele may already have an agreement in place with another club, but that is something Sissoko is keen to deny.
“We don’t know what we are going to do. Nothing has been finalised.
“But the leaders are losing Ousmane by themselves.
“From the start we have shown we want to discuss, with conditions of course, but without closing the door.”
Barcelona could still look to sell Dembele this month if he does not sign a new deal, but it is unclear if the player would agree to go.