Chelsea's inability to sign Jules Kounde this summer was down to their failure to meet the defender's release clause, Sevilla have confirmed.
Thomas Tuchel was keen to bolster his backline ahead of his first full season in charge at Stamford Bridge.
Kurt Zouma left the Blues to join West Ham, leaving Tuchel with one fewer centre-back in his squad.
The ambition was to replace Zouma with Kounde, and the 22-year-old was expected to go straight into Chelsea's first-choice starting XI.
But the European champions were unable to get a deal over the line after Sevilla changed tack during negotiations.
Chelsea thought a bid of £42.8m would be sufficient to prise the central defender away from the Estadio Ramon Sanchez Pizjuan.
However, Sevilla then decided they were not prepared to sell Kounde unless his release clause was triggered.
That would have required Chelsea to cough up around £68m for the France international.
"Kounde in the end has stayed because the club has decided that it was the right thing to do based on the evaluation of the offers they may have had, " Sevilla manager Julen Lopetegui told Diario de Sevilla.
"For me, as a coach, that Jules stays is positive. With the evolution he has had in these two years, it is positive, without any doubt.
"We trust that he'll continue to grow with us and, above all, perform, which is the most important thing."
Chelsea could return for Kounde next summer, with Sevilla highly unlikely to consider selling one of their star players in the January window.
If the Blues are unlucky with injuries this term, they could find themselves short of options in the heart of the backline.
Tuchel's pool of centre-halves includes Thiago Silva, Cesar Azpilicueta, Andreas Christensen, Antonio Rudiger and Trevoh Chalobah.
Chalobah is relatively inexperienced at Premier League level, though, and Tuchel would no doubt have preferred another senior option at the back.
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