It is understood that the Sanofi board has agreed that in principle the offer could be raised, but is waiting on a signal from Genzyme that the company is prepared to come to the negotiating table.
The news comes after Genzyme last week rejected an all-cash $18.5bn offer from Sanofi.
The US firm’s chief executive Henri Termeer said he did not believe it likely that the situation would turn hostile, but added that “a deal will only get done when the strategic value of the company is properly recognised”.
Analysts believe that a sweetened offer of around $75-$78 per share would be favourably looked upon by the Genzyme board.
Genzyme’s appeal lies in the growth potential of its drugs treating rare genetic diseases and a pipeline of new treatments, including one for multiple sclerosis. However, the complexity of the deal and the firm’s manufacturing problems mean negotiations could drag on.