Sanofi's board ousted its chief executive of six years at a special meeting on Wednesday, two days after it emerged he had fallen out with the French drugmaker's chairman, wiping more billions off its market value.
The board said Sanofi would continue the strategy of international expansion pursued under Chris Viehbacher, blaming his dismissal on poor relations between the CEO and the board.
But investors fear Sanofi may become more insular.
"Viehbacher tried hard to change the DNA of the company but the board won in the end. Sanofi will become more parochial now," said Navid Malik, head of life sciences research at Cenkos Securities in London.
Sanofi said Chairman Serge Weinberg would take on the CEO role until a replacement for the ousted German-Canadian Viehbacher was found. Weinberg said on a conference call that there had already been contacts with potential candidates.