Juan Antonio Samaranch Jr believes his father could play a key role in winning the 2012 Olympics for Madrid.
Samaranch senior, who was International Olympic Committee president for 21 years, is in Singapore to help drum up support for the Spanish bid.
"I can tell you my father has been very influential in the bid of Madrid," his son, part of the Madrid team, revealed.
"He's probably one of the people in the world, not only in Spain with the most Olympic experience."
But Samaranch Jr, himself an IOC member, insisted no deal had been done for Madrid and London to transfer votes to each other if either drops out of the vote first.
"It's beyond belief - something that technically cannot happen. It's difficult enough for me and Madrid and London to try to rally votes for our own project," he said.
"Can you imagine I can ask anybody, if I'm out, what he should do with his vote?
"I wish I had a basket of 20 or 30 votes to trade with anybody. Unfortunately the only vote with which I will be able to trade is my own."
Wednesday's vote will take place in rounds, with the city gaining the least support dropping out each time until one has an absolute majority.
Reports had suggested Samaranch senior could be an influential figure in persuading voters to switch allegiance to London if Madrid dropped out.
But his son emphasised he had only been acting as a supporter for Madrid's bid, and would not be aggressively lobbying in the final day before the vote.
"He's given us a lot of advice throughout the process, even in the design of the project itself. It's athlete-centred and that was his own original idea," he added.
"He's going to be very important and he has already been important.
"He was president for 21 years and was very neutral at that time.
"His job in helping Madrid has been publicly announcing that he'd be happy and inspiring us in the design of the project.
"But certainly it's not his responsibility to go and look for the vote. It's up to other people like me to try to get it done."