The tie is scheduled to be played at Vicarage Road on the weekend of January 13-15.
However, it has been suggested that the match will be played at either the Newlands Stadium or the Cape Town Stadium, which was built for the 2010 World Cup.
The proposal has not yet received official endorsement from the European Rugby Cup, the Rugby Football Union or the South African Rugby Football Union, but it is thought that no parties are opposed to the request.
"The idea of playing one of our Heineken Cup matches in Cape Town has been mooted, and it is appealing in many ways, but our first obligation is to protect the interests of our supporters," said Saracens chief executive Edward Griffiths.
The club have already confirmed that their tie against Ospreys in December will be played at Wembley Stadium.