Fifa will decide on the location of the 2018 World Cup on 2 December
Qatar's hopes of hosting the 2022 World Cup have suffered a setback with a confidential Fifa report rating their bid a high overall risk.
The Middle Eastern country is one of five contenders vying to stage the tournament, along with Australia, South Korea, Japan and the United States.
Australia and South Korea have emerged with the best assessments.
The US and Japan have been ranked as a medium legal risk after their failure to secure government support.
The hot weather in Qatar in June and July is one of Fifa's concerns about the country's suitability.
In part of the evaluation report which has been made public, Fifa said playing the competition in the two hottest months had to be "considered as a potential health risk for players, officials, the Fifa family and spectators, and requires precautions to be taken".
Fifa's assessment of the 2018 and 2022 bidders took place between July and September and focused on levels of government support, accommodation, transport, technology infrastructure and the security implications of each bid.
On the US and Japan bids, Fifa said: "...the necessary government support has not been documented as neither the government guarantees, the government declaration nor the government legal statement have been provided in compliance with Fifa's requirements for government documents..."
But US bid executive director David Downs said: "We have been in conversations with Fifa about this and they are comfortable with the situation."
Australia is bidding to become the first Oceania country to host a World Cup, while Japan and South Korea are hoping to host the tournament on an individual basis after jointly staging the 2002 event.
The concern over their three bids is the level of revenue.
"There is a risk of reduction in TV income from Europe," said Fifa. "The income from Asia/Oceania would need to be increased substantially to offset the likelihood of loss of revenue in Europe."
The vote to decide the hosts for the 2018 and 2022 World Cup hosts will take place on 2 December.
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