Sanofi-Aventis has sent Genzyme a letter indicating its interest in buying the company and the two sides are discussing the offer, a source familiar with the situation said on Monday.

The source familiar with the situation also said that Genzyme was not likely to accept a deal under $80 per share. Sanofi had been expected to send a formal bid for Genzyme over the weekend, but no details on the price or the structure of a potential deal were immediately available.

Sanofi's board last week authorized the company to press ahead with a formal offer for Genzyme worth up to $70 per share, or $18.7 billion, sources told Reuters at the time.