Interbrew, maker of Stella Artois, has said it does not intend to make an immediate bid for SAB.
But the Belgian Brewer refused to rule out a takeover bid within the next six months after an agreement to relax Takeover Panel rules.
The rules normally forbid a potential buyer returning to the table within six months after a denial.
However Interbrew has not submitted a formal bid.
The news of its interest emerged last week after bid research documents were leaked to several national newspapers. Also contained in the papers, which were sent by DHL courier from a location in central Europe, were forged bid proposals that stated an offer of 600p-a-share would be tabled in early December.
The Belgian brewer insisted the research on SAB, prepared by Goldman Sachs and Lazard, had been at an early stage. It was a clear attempt to sabotage any potential future bid.
The Takeover Panel has now launched an investigation. The panel is keen to trace the source of the leak and to determine the motives of the sender. Belgian authorities are also investigating as are Goldman Sachs and Lazard.
If Interbrew does successfully press ahead with a bid for SAB, it would be the latest in a string of acquisitions made by the Belgian brewer. Last year it bought Bass Brewers for £2.3bn and more recently, Beck's for £1.2bn.
It is understood that Interbrew is worried that if it does not attempt a deal, it could miss out on the global consolidation in the sector. It fears a rival merger of Scottish & Newcastle, Miller Brewing of the US and SAB would leave it out in the cold.
A merger between Interbrew and SAB would make strategic sense. Interbrew operates mainly in Europe while SAB is focused on emerging markets such as China. SAB also controls 98 per cent of the South African market. A merger would create a £12bn company.
Consolidation is definitely on the agenda at SAB. Chief executive Graham Mackay recently said he envisages a future where his company will merge to become the Coca-Cola of the beer world.