Barcelona have agreed a £65.4m fee to sign Rodri from Man City, who could now go in for Chelsea's Enzo Fernandez, who is worth £120m according to his club. But why does the Argentina player have a much higher transfer value?
Rodri is a four-time Premier League title winner who was named player of the tournament at the World Cup with Spain. And yet Chelsea are demanding almost twice as much for Fernandez.
In this edition of Between the Lines, the Your Site strand unpicking the data behind football's biggest stories, we explain what goes into player transfer valuations as this summer's spending continues.
Rodri's outstanding World Cup performances for Spain, following two injury-hit seasons with Manchester City, proved the former Ballon d'Or winner is still capable of operating at his best level.
Even in a disrupted Premier League campaign last term, data from Gradient Sports shows Rodri outperformed Fernandez in five out of six key midfield metrics, including passing, carrying and tackling.
Rodri's age, however, having turned 30 at the start of the summer, puts him at a different stage of his career to Fernandez, who is heading into what should be his peak years at 25.
Factoring current Premier League midfielders who have reached a Transfermarkt value of £35m at some point in their careers, the graphic below shows that, on average, values peak at 27 before beginning a steady decline as players head towards their 30s.
Rodri is atypical in that, according to Transfermarkt, his value peaked later, at the age of 28, when he won the Ballon D'Or. But it has subsequently dropped dramatically, from £111.1m to £47m.
Fernandez's Transfermarkt value, by contrast, is at its highest point having risen to £85.5m, seemingly following the established trend.
Contract length is another important factor in player valuations, both in relation to Rodri and Fernandez, and more broadly.
Rodri had moved into the final year of his contract, meaning Manchester City ran the risk of losing him for nothing next summer, while Fernandez has six years remaining on his deal at Chelsea, putting his club in a much stronger negotiating position.
Grouping current Premier League players by contract lengths clearly shows that the longer the contract, the higher the average value.
According to Transfermarkt valuations, players with five or more years on their contracts, such as Fernandez, have an average value of £49.7m. Players with under a year remaining on their contracts, such as Rodri, have an average value of just £7m.
It's also worth noting that Transfermarkt's valuations only factor contract lengths to a limited extent, meaning the true impact on valuations could be even greater than the data suggests.
By correlating Premier League player profiles and Transfermarkt transfer values, we found that age and contract runway rank as the two biggest factors in determining player value.
The other contributing factors, according to our analysis, are short and long-term player form, club strength, quantified by Opta's power rankings, and recent availability, measured by minutes played.
So, while Rodri has the superior performance record, both short and long-term, Fernandez comes out favourably in areas more impactful to transfer value such as age and contract length.
Fernandez also has a far better availability record, with Rodri penalised for playing only 1,515 of a possible 3,420 Premier League minutes last season compared to Fernandez's 3,121.
Fernandez's relatively clear injury history is another factor which helps to explain why he has a far higher transfer value than Rodri, despite the Manchester City midfielder being the better performer.
Transfer values are not an exact science. Valuations and actual transfer fees can differ significantly depending on the given context. Last summer's window, for example, featured strikers moving for inflated fees due to demand outweighing supply.
Asking prices for players in specific positions are often benchmarked against recent moves. This summer, for example, Chelsea will be factoring the fees paid by Spurs, Manchester City and Arsenal for central midfielders Mateus Fernandes (£85m), Sandro Tonali (£100m), Elliot Anderson (£116m) and Bruno Guimaraes (£75m) in their valuation of Fernandez.
The context helps to explain why Chelsea are able to set an asking price of £120m for the Argentina international, despite his Transfermarkt valuation sitting much lower, at £85.5m.
This 'snowball' effect has contributed to transfer fees rising at a far higher rate than inflation, pushing the average cost of a top-level signing up from £53.9m to £61m in a year.
Premier League clubs are also showing a willingness to pay a premium for Premier League-ready players, due to the ever-increasing physical demands of the competition, which may help to explain why Chelsea feel Fernandez is worth more than the £107m they paid to sign him from Benfica three years ago.
