AstraZeneca chairman Leif Johansson has said he believes Pfizer's £69 billion takeover bid is their final offer.
"They say it is their final bid so I have to believe them," he told BBC Radio 4's Today programme.
AstraZeneca has urged its shareholders to reject the offer.
Mr Johansson said the Pfizer bidding had been "controversial from the start" but it was up to shareholders to decide on its fate.
He said the Pfizer offer was "too low", would prove "too disruptive" to Astra's ability to deliver drugs to the market and presented too much of a "risk".
Pfizer has until Monday until it admits defeat in bidding for AstraZeneca. But after the shenanigans of the past few days we cannot be sure.
AstraZeneca's share price is tumbling back down to earth after the board rejected a "final" Pfizer bid. So is the takeover really over?
Sweden's Finance Minister says the Government should be "very, very sceptical" about any promises the US pharmaceutical giant makes.