The brewing groups said that there was no guarantee an offer would be made but they plan for Heineken to take control of S&N's business in the UK and some other European markets, with Carlsberg taking charge of the rest of the company.
This includes S&N's East European brewer Baltic Beverages Holding and its businesses in France and Greece.
Shares in S&N jumped 16% following reports of the interest in the brewer.
S&N's brands include Foster's, Newcastle Brown Ale and Kronenbourg.