Bayer, the German aspirin-to-weed-killer conglomerate, was putting the finishing touches on Sunday night to a $46bn-plus all cash offer for Monsanto, which it could unveil to the market as early as Monday morning Europe time, people familiar with the matter said.

The purchase of the US agribusiness, which would be the biggest outbound German takeover since carmaker Daimler-Benz acquired Chrysler for $38.6bn in 1998, would create a global juggernaut in the business of providing everything from seeds to crop chemicals to farmers.

Any deal to acquire Monsanto is expected to value the St Louis-based company at a premium to its market value of nearly $46bn at the close of last week, according to people close to the process. They warned that the situation and timing remained fluid.