After their worst season in nearly 30 years, Chelsea have never had a more critical summer in terms of transfer business.

Departures are likely to prove as crucial as new signings and there has been plenty of movement in both directions, with expectation that more business will take place throughout the window.

The PA news agency looks at what has been done and what to expect ahead of Mauricio Pochettino’s first season in charge.

How urgent is it all?

Very. Chelsea have a bloated first-team squad following owner Todd Boehly’s scattergun first 12 months at the helm, with more than £600million spent on transfers.

Successive managers in Graham Potter and Frank Lampard admitted to finding the job of accommodating so many players an almost unworkable challenge, and since January there has been little consistency in team selection or shape.

There is also the matter of satisfying Financial Fair Play rules. With sky-high outgoings and no income from European football, something has to be done to balance the books.

Chelsea have so far confirmed the sale of nine players since the window opened last month.

Who’s on the way in?

Christopher Nkunku has joined from RB Leipzig for £53m after a pre-contract agreement was reached in January for the France international.

With the team having recorded their lowest goal tally in almost a century last campaign, Villarreal’s Nicolas Jackson has also been added to Pochettino’s attacking options.

Moises Caicedo of Brighton is a long-term target but no bid has been made since the Seagulls rebuffed Chelsea’s repeated overtures in January.

Pochettino is reported to have turned his attention to France Under-21 and Lyon winger Rayan Cherki as a replacement for Christian Pulisic.

Who has already left?

Chelsea have raised eyebrows with the amount of outgoings from Stamford Bridge in the last month, which has allowed Pochettino to streamline his bloated squad ahead of their pre-season tour to the US.

N’golo Kante accepted a reported £86m-a-year offer to become the latest star name to swap a major European club for Saudi Arabia.

Defender Kalidou Koulibaly was in and out of the team during his one season in blue and left for Al-Hilal less than 12 months after joining from Napoli.

Mason Mount’s contract saga came to an end when he penned a five-year deal with Manchester United in a move away from his boyhood side.

Edouard Mendy’s three years in west London came to an end when he made the move to Saudi side Al-Ahli after falling behind in the goalkeeper pecking order to Kepa Arrizabalaga.

Kai Havertz signed for Mikel Arteta’s Arsenal for a reported £65million, while Mateo Kovacic was picked up by Pep Guardiola’s treble-winning Manchester City on a permanent deal as a replacement for club captain Ilkay Gundogan.

Captain Cesar Azpilicueta also bid farewell to the club after 11 years of service, while Ruben Loftus-Cheek and Pulisic joined up with former teammates Fikayo Tomori and Olivier Giroud at AC Milan.

Who will be next?

Hakim Ziyech’s move to Al-Nassr fell through at the last minute and Chelsea will still be keen to shift the unwanted winger before the window closes.

Conor Gallagher has attracted interest from a number of potential suitors but the 23-year-old could be vital for Chelsea next season, with midfield options looking short after this summer’s fire sale.

Brighton could bid again for Levi Colwill after his stellar performances in England’s European Under-21 Championship campaign – the young centre-back is yet to commit to a long-term deal.

Who else is surplus to requirements?

Striker Romelu Lukaku is eager to return to Inter where he spent last season on loan, though Chelsea have reportedly been unwilling to agree to another temporary move as they seek a permanent transfer.

Pierre-Emerick Aubameyang is another outcast to have been linked with the Saudi Pro League and is unlikely to have a future at Stamford Bridge, though it is thought he remains unconvinced about a move to the Gulf.

Callum Hudson-Odoi and Chelsea could part ways this summer but there has been no concrete interest from potential clubs after the winger’s underwhelming loan spell at Bayer Leverkusen.