Sevilla have rejected an offer, presumed to be from Chelsea, for Jules Kounde.
The Blues are keen to sign the France international before the transfer window closes at 11pm BST on Tuesday.
Kounde, who was previously a target for Manchester United, is thought to be open to a move.
But Chelsea are running out of time to tie up a deal for the 22-year-old, who was one of La Liga's standout defenders last season.
Sevilla have confirmed they received an offer for Kounde this week, thought to be in the region of £43m.
But the Spanish side rejected that bid and remain keen to keep hold of the centre-back.
"It is true that there was an offer for Kounde that we turned down," club president Jose Castro said.
"Right now there is no concrete offer for the player. If it comes, we will look at it as we always have done. If we have to [sell], we will do, as long as those resources can be re-invested in the club to keep improving and expand our trophy cabinet.
"While the market is open, anything can happen. We have players who could leave. Anything can happen this time of year until the 31st [August]. It is a window where there have been few moves in most clubs, but not in ours."
Every player in La Liga has a release clause in his contract, and Kounde's is set at £77m.
Chelsea had hoped that Sevilla would negotiate a smaller fee but the two parties remain some way apart.
Los Nervionenses believe they could challenge for the La Liga title this season and are determined to have the strongest squad possible beyond the end of this month.
Kounde is under contract until 2024 and Sevilla are under no financial pressure to sell.
Chelsea could have their work cut out in trying to sign the 22-year-old in the coming days.
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