Headlines on Friday afternoon suggested a move for the 24-year-old had already been completed, but the London club have told Sky Sports News that no such deal has been reached.
While a number of Barcelona players have already begun celebrating the signing on Twitter, goalkeeper Victor Valdes said the move was still not official.
"If the news is confirmed it will be great news, above all for one person, a friend, and the Barcelona fans," he told AS.
"I'm not disclosing anything, but as you know it is advanced, and although it is not official it will surely be closed very soon."
Barcelona boss Pep Guardiola is understood to have told the midfielder to remain in England until after the weekend, with the Catalan club scheduled to face Real Madrid in the Spanish Super Cup on Sunday.