Fifa is expected to make 2018 and 2022 World Cup decisions on 2 December
Spain and Portugal have denied allegations they agreed a pact with Qatar to manipulate the voting process for the 2018 and 2022 World Cups.
Fifa is investigating claims of collusion between the two bids, which could lead to disqualification.
But Miguel Angel Lopez, chief executive of the Spanish/Portuguese candidacy, said: "We told Fifa we do not have any agreement with another bidding nation."
Spain/Portugal is bidding for the 2018 tournament, with Qatar going for 2022.
The Iberian bid has offered world governing body Fifa full cooperation in its investigation, Lopez added.
Fifa president Sepp Blatter: "Our society is full of devils, and these devils, you find them in football"
The probe is part of a wider inquiry by Fifa into alleged breaches of the bidding rules.
Fifa's investigation will run alongside the ethics committee's probe into two senior Fifa officials who have been provisionally suspended after being caught up in a World Cup cash-for-votes scandal.
Amos Adamu from Nigeria and Tahiti's Reynald Temarii, both members of Fifa's 24-man executive committee which will decide on the 2018 and 2022 World Cups, were trapped by a Sunday Times undercover investigation in which they appeared to offer their votes in return for payment.
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