In a letter to Genzyme CEO Henri Termeer released Monday, Mr. Viehbacher said his preference is still to strike a friendly deal. Indeed, for various reasons, the deal ultimately has to gain the approval of Genzyme's board before it can proceed.
But should Sanofi gain acceptance from enough Genzyme shareholders—especially if, as expected, it boosts its offer—it could become more difficult for Genzyme's board to withhold its approval. And in a conference call with analysts Monday, Mr. Viehbacher didn't rule out the possibility of ultimately seeking to oust Genzyme's board.