FIFA have become embroiled in a series of legal disputes with the Qatari authorities with relations between the two main World Cup organizers at an all-time low as the tournament reaches the knock-out stages.

Sportsmail has learned that throughout the World Cup FIFA have sent several legal letters to Qatar's Supreme Committee and are awaiting formal responses.

The legal letters are understood to relate to contractual issues that have arisen before and during the tournament, and will ultimately boil down to a battle over financial liability.

FIFA's official beer supplier Budweiser are owed compensation after the Supreme Committee dramatically withdrew the sale of alcohol from stadiums 48 hours before the opening game between Qatar and Ecuador, while there are numerous other issues to resolve involving other World Cup suppliers.

Tension between FIFA and the Supreme Committee was evident on Thursday in their contrasting responses to reports of the death of a migrant worker at Saudi Arabia's base camp during the group stages, as revealed by The Athletic.

Whilst FIFA said they were 'deeply saddened by this tragedy' and offered 'sympathies and thoughts to the workers family,' the Supreme Committee said the incident took place on property outside their jurisdiction and have passed the matter on to the Qatari government.

Supreme Committee chief executive Nasser Al Khater even made the extraordinary comment that death was a natural occurrence.

'Death is a natural part of life, whether it's at work, whether it's in your sleep,' he said.

'We're in the middle of a World Cup. And we have a successful World Cup. And this is something you want to talk about right now?'

FIFA declined to comment on their legal issues with the Supreme Committee.