Chelsea's signing of Mykhailo Mudryk took their spending this season past the £400m mark with two weeks to go before the end of the latest transfer window.
That comes after a summer in which they spent a Premier League record £270m - the second-highest summer spend by any club in the world after Real Madrid (£292m) in 2019.
So how can they afford to keep spending, and how do the numbers work with regard to Financial Fair Play rules? BBC Sport takes a closer look at the sums.
There are two sets of rules that Chelsea have to adhere to - the Premier League's profit and sustainability rules and, as they regularly play in European competition, Uefa's Financial Fair Play regulations (FFP).
Premier League profitability and sustainability rules allow for total losses of £105m over a three-year period. Any club that posts losses in excess of that figure could face penalties, including large fines or even a points deduction.
Under Uefa's current rules, clubs can spend up to 5m euros (£4.4m) more than they earn over a three-year period. They can exceed this level to a limit of 30m euros (£26.6m), if it is entirely covered by the club's owner.
Uefa has a wide-ranging list of potential punishments for clubs which break these rules - such as Wolves in 2020 - from warnings, fines or even the loss of European titles.
However, new Uefa rules introduced in June limit clubs' spending on wages, transfers and agents' fees to 70% of their revenue, though permitted losses over a three-year period have risen to 60m euros (£49.96m).
Clubs have been given three years to implement these changes.
Football finance expert Kieran Maguire estimates that Chelsea only had a three-year FFP loss of £5m in their most recent accounts, which go up to 2021, so have a fair amount of leeway in terms of permitted losses.
Kieran Maguire on BBC Radio 5 Live's Monday Night Club
There are two issues: can they afford it in terms of cash? They can because they are buying players and paying for them in instalments. So the finances of the club itself are fine.
With regards to Financial Fair Play, the accounting is more Harry Potter than Graham Potter in the sense that it's quite weird and wonderful.
When you buy a player, you spread the cost of the player over the life of the contract. If we take a look at Mykhailo Mudryk, they bought him for £89m and he is on an eight-and-a-half-year contract. When you sell a player, all of the profits are taken into the accounts immediately [even if actual payments are made in instalments]. We have got the sales of Tammy Abraham and Fikayo Tomori. That was £77m worth of profit.
They also won the Champions League, they won the Uefa Super Cup, they won the Fifa World Club Cup and all of that was extra money coming in. So things aren't as bad as I think some of the commentators are making out.
Football finance expert Kieran Maguire:
It's a very high-risk strategy.
If the players turn out to underperform, you have then got a player on a total salary cost of £7m or £8m a year and you are committed to that for seven to eight years. No other clubs are willing to take that wage off your hands for such a long period of time. So you've got four or five players who are happy to sit down for the rest of the contracts. They are even taking up space on your 25-man roster as far as Uefa is concerned or they are tying up space on your payroll.
If they are fantastic players, it is great because it means that if Real Madrid come calling in two years' time, you have still got five or six years remaining on the contract and can extract the maximum fee.
Kieran Maguire to Sky Sports:
It would be restrictive. If you take when Chelsea won the Champions League in 2021, they generated around 120 euros (£106m) in prize money. You can expect to make £3-4m per home game plus bonuses from sponsors.
Compare that to the Europa League. For every £1 you make in that competition, you are making around £4.50 in the Champions League, so there will also be a significant effect if you don't qualify.
