Sky Sports News can reveal two emails that appear to prove West Ham did make offers to Sporting Lisbon for William Carvalho.
The Hammers are pursuing legal action against Sporting's communications director Nuno Saraiva after he claimed the club received no proposals from the Hammers for Carvalho, while also making a string of controversial remarks about West Ham co-chairman David Sullivan.
The emails appear to show Sullivan offering just under £23m for Portugal midfielder Carvalho before making a follow-up bid that included a 10% sell-on clause and additional add-ons based on West Ham qualifying for the Champions League.
Sullivan also claimed last week that the offers were rejected before Sporting got back in touch with West Ham on Deadline Day and indicated a willingness to negotiate another deal, but there was not enough time.
But Saraiva said on Facebook: "No proposal arrived for the player William Carvalho.
"Mr Sullivan has a duty to prove what he says. For this reason, Sporting Clube de Portugal challenge him to publicly show the proposals he says have been made, as well as the evidence that Sporting CP has received them."
Sky Sports News understands Carvalho wanted a move to the Premier League but he had a £40m release clause in his contract and Sporting were initially keen for that figure to be met.