The Rojiblancos can sign players, they cannot however register them to play until January 2018.
His relationship with Antonio Conte has deteriorated to the extent that the Brazilian-born striker expects to be omitted from Chelsea's pre-season tours.
Costa's time at Chelsea effectively came to an end via a text message sent from Antonio Conte.
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Conte, who previously managed Juventus in Serie A, turned down an offer to move back to his home country to take charge of Inter Milan this summer.
The 47-year-old is now on holiday in Italy and is close to securing a new home close to Chelsea's training ground ahead of his wife and daughter's move to join him in London. Chelsea are preparing to add to their squad despite winning the Premier League title last season. Lewandowski has just one goal behind striker Dortmund "Borussia" Pierre-Emerick of Forward.
Chelsea have agreed to sign Manchester City goalkeeper Willy Caballero on a free transfer which will be announced on July 1, while they are hopeful of signing Tiemoue Bakayoko for a fee in excess of £40 million (S$70.2 million). He also played a key role in guiding the Madrid outfit to a UEFA Champions League final.
It leaves Conte stuck with Costa until at least January and, while he is a very popular character within the changing room, the Italian is concerned that the unrest could fester and sour the atmosphere in the club.