Chelsea have made progress in talks to sign Moises Caicedo but Brighton are now holding the London club to a demand of £90m basic fee.
The Blues would then have to add a further £10m to be made up in bonuses and expected clauses.
The saga has continued with little movement throughout the summer, as Chelsea have proven reluctant to go beyond £80m.
While Brighton, who rarely deviate from their initial asking price, have seen the nature of the talks revolve around pushing Chelsea to go closer to their valuation.
There has now been some breakthrough on the structure of a potential deal though, but the expectation is that the Stamford Bridge hierarchy will eventually have to go further and make a £90m-plus offer.
Chelsea are hoping to get it done before Sunday's season opener at home to Liverpool, as Mauricio Pochettino is eager to add more energy to his midfield.
Chelsea have meanwhile made a £48m bid for Romeo Lavia, as they hope to beat Liverpool in the race for the the 19-year-old Southampton midfielder.
Pochettino may look to partner Enzo Fernandez with Conor Gallagher to take on Jurgen Klopp’s side following a string of departures this summer.
The Blues lost N'Golo Kante on a free transfer, Mateo Kovacic joined Manchester City and Ruben Loftus-Cheek signed for AC Milan.
Mason Mount, who would ideally not have played so deep for the Blues anyway, joined Manchester United, while Denis Zakaria departed after his loan expired, returning to Juventus.
Nonetheless, the Blues have a number of youthful options, with Lesley Ugochukwu signed from Rennes, Carney Chukwuemeka and Andrey Santos, who arrived this summer after returning to Vasco da Gama on loan following a deal to sign the Brazilian in January.
Caicedo’s arrival would also allow Fernandez to push further forward and influence the game in the final third.
The Argentine World Cup winner swapped the No.5 jersey for the coveted No.8, previously worn by Frank Lampard, this summer.
Moises Caicedo is a key target for Chelsea this summer— (Getty Images for Premier League)
