A senior figure at Sporting Lisbon has rejected David Sullivan's claims regarding West Ham's pursuit of midfielder William Carvalho, insisting that the Hammers' co-owner is a "liar" and has compared the saga with the pornography business.
The Hammers pursued Carvalho in the final weeks of the transfer window, though they were unable to strike a deal for the Portugal international, which would have amounted to a club record.
Sullivan, West Ham's co-president, claimed that Sporting chose to accept the offer - of roughly £35 million - on deadline day, but that the Hammers opted not to go ahead with the deal as they were unable to put Carvalho through a medical.
"It is no secret that we made a club-record bid for Sporting Lisbon's William Carvalho but unfortunately that offer was rejected a couple of weeks ago," he said.
"Late last night [Thursday] Sporting Lisbon made contact to accept the original offer, but unfortunately it was just too late in the day, and we simply did not have enough time to put the player through a medical.
"We were not prepared, as a club, to buy a player for that amount of money without him having gone through adequate medical checks."
However, Sporting's director of communications, Nuno Saraiva, has lambasted Sullivan's comments and challenged him to prove his claims.
"Mr David Sullivan lies. Sporting Club de Portugal, as was said by its president, did not receive any proposal for the player William Carvalho," he wrote on Facebook.
"The football industry is not the stage of an adult film in which all obscenities are allowed.
"For this reason, the owner of a club requires much more than this intellectual pornography. Mr Sullivan has a duty to prove what he says.
"For this reason, Sporting Clube de Portugal challenges him to publicly show the proposals he says have been made as well as the evidence that Sporting CP has received them."