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 the bulk of the activity is still to come.

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

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, with cohesion amongst the squad lacking.

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, ideally before the June 30 deadline for keeping everything on last season’s accounts.

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, more attacking arrivals are necessary, and a deal for Villarreal’s Nicolas Jackson has reportedly been struck.

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

So far the departures have been predictable ones, with N’Golo Kante leaving for Al-Ittihad and Kalidou Koulibaly joining Al-Hilal, both in the Saudi Arabia Professional League.

Kante had looked close to agreeing a new contract at Stamford Bridge last season but talks had long since broken down by the time he accepted a reported £86m-a-year offer to become the latest star name to swap a major European club for the Gulf.

Defender Koulibaly was in and out of the team during his one season in blue, and with manager Pochettino well stocked in central defence he has left the club less than 12 months after joining from Napoli.

Deals have been agreed for forward Hakim Ziyech and goalkeeper Edouard Mendy to join their former team-mates in Saudi Arabia for £8m and £16m respectively.

Ziyech has been eager to depart since a deadline-day move to Paris St Germain fell through in January, after Chelsea failed to submit the correct paperwork in time.

Despite a strong first two seasons in west London, Mendy has lost his place as first-choice keeper to Kepa Arrizabalaga.

Kai Havertz is on the verge of joining Arsenal in a reported £65m deal, with an announcement expected this week, while Mateo Kovacic will join Manchester City after the clubs agreed a £30m fee for the Croatia international.

Striker Romelu Lukaku is eager to rerun 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.

As it stands, Manchester United have had three bids for the England midfielder rejected and are at the point of walking away from the deal to focus on other targets.

The 24-year-old rejected new terms last season but there is no offer on the table from the Blues, with his contract about to enter its final 12 months.

United reportedly believe an asking price of £65m is too high for a player who will be available on a free this time next year and can begin negotiating a pre-contract agreement with another club in January.

That leaves the player with three options: see out the final year of his deal, hold out to see if another bidder emerges, or ask Chelsea back to the negotiating table.