AstraZeneca Chief Executive Pascal Soriot said his company's board would be obliged to consider a compelling offer from Pfizer, despite rebuffing the U.S. drugmaker's approaches so far.
"It's impossible to say we would never accept any offer," he told a committee of British lawmakers on Tuesday.
"We are very well aware of our fiduciary duty and an offer that would value the company at the right value and would basically be an offer and a proposal that we would find implementable without execution risk - or with execution risk that we could manage - such an offer we would have to consider."
The U.S. drugmaker has stirred up a political storm with its $106 billion plan to acquire AstraZeneca.
The deal would be the largest foreign takeover of a British firm and is opposed by many scientists, trade unions and politicians who fear for British science jobs given Pfizer's track record of cost cutting after past acquisitions.