Everton want to restructure their deal for FC Twente midfielder Leroy Fer over fitness concerns.
PA Sport says during his medical, Everton doctors identified an issue which raised enough concerns for them to go back to Twente in an attempt to renegotiate the deal.
Instead of the full fee up front the Premier League side wanted to pay a smaller amount with the remainder dependent on appearances and other factors.
Twente have rejected the new terms and although negotiations are continuing the move is in the balance.