Maurizio Sarri has a tough job on his hands at Stamford Bridge. 

It will be no easy task to get the Blues to catch up with their competition. Other clubs have strengthened, whilst Chelsea have thus far only brought in Jorginho and Robert Green.

Chelsea won an FA Cup last season, but it was an underwhelming season. Stamford Bridge is certainly not the fortress it once was. Clubs such as Arsenal and Liverpool have strengthened heavily, making even breaking back into a Champions League spot a tough ask for new boss Sarri.

Sarri is engaging in a race against time to get his side ready for the start of the season. The Antonio Conte situation dragged on for far longer than most Blues fans would have liked.

Maurizio Sarri will want to bring his own players to South-West London and put his stamp on the side. Time is running out for Chelsea to bring in new additions with deadline day fast approaching.

With that in mind, here are two players Sarri will be fuming Chelsea haven't signed this summer...

Kalidou Koulibaly is a player Maurizio Sarri will be very familiar with from his time with Napoli.

The giant 6ft 5 centre-back is one of the best defenders in Serie A. The man mountain was a huge figure in a Napoli side who pushed a mega-rich Juventus to the wire for the Italian title.

He is not just a big unit, who will win everything in the air. He is a calm and composed modern day centre-back, who at 27-years-old is in his prime. Defence is a key area in which Chelsea need to tighten up, they were unconvincing at the back to say the least last season.

Sarri will be scratching his head wondering why Chelsea have not done absolutely everything in their power to bring in Koulibaly.

Sarri will be fuming the club has not tried to re-sign 29-year-old former Blue Diego Costa.

His expensive replacement, Alvaro Morata, just did not cut it in the Premier League in the way in which Chelsea hoped. The aggressive and tenacious Diego Costa was a huge miss. His battle and fight was a huge miss up front, his presence alone created space for players like Eden Hazard to really show their best.

Diego Costa is valued at £54m by Transfermarkt.

Chelsea should have done everything to re-sign the Spaniard.