But Brighton's official Twitter account posted a message that no deal had been done an hour later.
"Contrary to inaccurate reports from numerous media outlets this evening, no agreement has been reached with any club to sell Marc Cucurella," it said.
Brighton were understood to be pushing hard towards a separate deal for Chelsea's highly-rated centre-back Levi Colwill.
Talks between the two clubs are understood to be ongoing over whether the deal for the 19-year-old would be a loan a permanent transfer.
Manchester City had appeared in pole position to sign Cucurella earlier this summer, but are understood to have refused to meet Brighton's valuation.
Cucurella's likely Chelsea move will take the Blues' summer spending past the £150million mark, with Raheem Sterling and Kalidou Koulibaly the other high-profile additions under Todd Boehly and Clearlake Capital's new ownership.
England Under-19 midfielder Carney Chukwuemeka and Chicago Fire goalkeeper Gabriel Slonina are the other new recruits already secured by the Blues this summer.
Chelsea will continue to press for further recruits, with another centre-back and a right wing-back still potential additions.
Cucurella's signature could also pave the way for Marcos Alonso's long mooted move to Barcelona.