Tottenham midfielder has been linked with an exit.
Dembele is popular player at Tottenham and is a favourite of manager Mauricio Pochettino.
He is currently in Belgium's preliminary World Cup squad and is hoping to earn a spot in the finals.
He even hinted that he hopes strong performances at the World Cup could lead to offers.
De Mul said: "Mousa has another one year contract with Tottenham, he has played a fantastic season and there is a lot going on around him, there is a lot of interest inside and outside of Europe, we are waiting for the World Cup and I hope he plays in Russia, because he deserves that after such a peak season.
"For the moment Mousa will not sign."
Dembele has been linked with an exit from Tottenham, with The Telegraph reporting he wants a three year deal at an increased salary, which would take him up until he is 35.
He has been linked with a move to the Chinese Super League, and this is a deal which could allow Spurs to get a top price for his signature if they do sell up.