A leading industry analyst said: "S&N is looking increasingly vulnerable."
He added that Anheuser-Busch or SABMiller were the most likely contenders, with other brewers, including Interbrew and Heineken, eyeing up S&N's assets abroad.
Potential buyers will also weigh up the benefits of S&N's purchase of Bulmers, which has won approval from Brussels.
It will be run as a separate division in Hereford with Willie Crawshay at the helm. S&N's pre-tax profit for the year to April 27 fell to £284.6m from £347m the previous year.
The UK beer division saw full-year operating profits decline by 9% due to ongoing issues with its supply chain. Beer volumes lagged behind the market in response to S&N's new policy of seeking value over volume.
>>p56 S&N review of Bulmers