Atletico Madrid are increasingly confident they have made a breakthrough in negotiations to sign Diego Costa from Chelsea, Sky Sports News understands. A source close to the negotiations says progress is being made but "it is not sorted yet", after a summer-long debacle between the player and his current West London employers. Atletico are banned from registering new players before January and have so far offered only half what Chelsea want for the striker, which has been £50m. Atletico have yet to offer more than £30m. Costa has been in self-enforced exile from the Blues since they won the Premier League title, and has made it clear he wants to rejoin Atletico after being told he was no longer wanted by Antonio Conte.