The latest allegations are not expected to lead to Qatar being stripped of the World Cup but they have placed renewed focus on the lengths the wealthy Gulf state may have gone to in its efforts to secure the competition.
According to The Sunday Times, the smear campaign included paying a professor £6900 ($13,300) to write a damning report on the economic cost of a World Cup in the US. Journalists, bloggers and high-profile figures were recruited in each country to build up concerns over the respective bids, the paper reported.
Fifa rules say that bidders must "refrain from making any written or oral statements of any kind, whether adverse or otherwise, about the bids or candidatures of any other member association which has expressed an interest in hosting the competition".
Qatar said it rejected all the claims made by the newspaper.
One of the leaked emails sent to Qatar's deputy bid leader Ali al-Thawadi shows the Gulf state was aware of a plot to spread "poison" against its chief rivals.
The leaked documents also revealed that a group of American PE teachers had been recruited to ask Congressmen to oppose a US World Cup on the grounds the money would be better spent on high school sports, the paper claimed.
Qatar was previously investigated by Fifa over allegations of corruption surrounding the World Cup bid but was cleared in 2014 following a two-year inquiry led by American lawyer Michael Garcia. He said that "for the most part, the bidding process was fair and thorough", despite certain "questionable conduct".