Two emails appear to prove West Ham did make offers for William Carvalho in light of denials from Sporting Lisbon.
The Portuguese club's communications director, Nuno Saraiva, has claimed no bids were received from the Hammers for the midfielder, adding that "[co-chairman] Mr [David] Sullivan has a duty to prove what he says."
David Sullivan Jr, son of the West ham co-chairman, confirmed on Twitter afterward that the club intends to take legal action against Saraiva.
Sky Sports have now obtained two emails, allegedly sent from Sullivan to Sporting, first offering £23million spread over three seasons before a second included a sell-on clause and potential add-ons should West Ham qualify for the Champions League.
West Ham allege the Sporting rejected the outlined offers before returning late in the transfer window to accept the terms, leaving little time to complete a deal.
Sullivan said earlier this week: "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 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."
