A British chemistry professor has calculated that if the World Cup trophy were really solid gold it would be too heavy for footballers to lift.
Martyn Poliakoff of Nottingham University estimates that a solid gold trophy of its size - 36cm (14 in) high - would weigh at least 70kg (154lb).
He concludes that the trophy, or at least part of it, must be hollow.
Fifa insisted that the metal part of the current trophy, which dates back to 1974, was "solid gold".
It told the BBC News website the prize weighed 6.175kg, including 4.9kg of "solid 18-carat gold" and two layers of the semi-precious stone malachite.
Nobody wins the coveted trophy outright as Fifa retains possession between tournaments, awarding a gold-plated replica to each World Cup champion.
Making his case on the university's Periodic Table of Videos website, Professor Poliakoff said a genuinely solid gold cup of this height would be "as much as the weight of quite a large adult".
"Gold is very heavy, it's one of the densest metals that there is," he said.
"According to my calculations, if it was solid all the way through, it would have somewhere between 70 and 80kg of gold in it."
The professor suggested the term "solid gold" might mean "the metal part is gold all the way through - it isn't that there is a thin layer of gold and the rest is steel, for example".
"However, I think - and I have no means of knowing - that perhaps the ball at the top, which is the world, is probably hollow... because I don't think that it would be light enough for people to wave above their heads, and also it would be a big waste of gold."
The professor added that he was "not very interested in football".
"I was a teenager when England won the World Cup in 1966," he said.
"I didn't watch the game then and I haven't watched a World Cup match since then, but perhaps I will watch something this year."