Grolsch is understood to have teamed up with venture capitalists CVC and Cinven to join the auction for the brewer, which closes on December 18. It was reported earlier that the same two venture capitalists had teamed up with the former head of Bass Brewing, Iain Napier, to launch a bid.
Grolsch also finds itself fighting a home turf war to win Carling as rival Dutch brewer Heineken is thought to have made a bid.
Other bidders believed to be in the race include Carlsberg Tetley, the UK arm of Danish brewer Carlsberg, and US and Canadian beer giants Coors and Molson have also been linked to bids.
The price for the business is likely to be high, with estimates ranging from between £1bn to £1.3bn.
Interbrew announced in September that it would sell the premium UK beer brand as part of a compromise deal worked out with the UK competition authorities, following its takeover of Bass Brewers. To comply with UK competition rules, a brewer can not control more than 30% of the market. Carling alone has a market share of 18%, while Carlsberg Tetley has 12%.
The UK secretary of state Patricia Hewitt ordered Interbrew to sell either Carling or Bass Brewers so that it would remain inside competition regulations.
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