Chelsea have identified four potential alternatives to Sevilla centre-back Jules Kounde, according to reports.
The Blues had been hoping to sign the France international this summer as they seek to revamp their defence.
Andreas Christensen and Antonio Rudiger departed Stamford Bridge when their contracts expired on June 30.
Chelsea have already completed the signing of Kalidou Koulibaly from Napoli this summer.
But they are still looking to acquire at least one more defender before the transfer window closes at the start of September.
Kounde was thought to be at the top of their wish list but the deal is in danger of collapse, according to the Guardian.
Chelsea have agreed a £55m fee with Sevilla but the player appears to prefer a transfer to Barcelona.
The La Liga giants stepped up their interest in the Frenchman over the weekend and are now in pole position to sign him.
The aforementioned report adds that Thomas Tuchel was never entirely convinced by Kounde, and Chelsea are now set to turn their attention elsewhere.
According to 90min, they have drawn up a shortlist of defensive targets which includes Villarreal's Pau Torres, Inter's Milan Skriniar, RB Leipzig's Josko Gvardiol and Dayot Upamecano of Bayern Munich.
It is possible that Chelsea will try to sign two members of that group, a development which would leave academy product Levi Colwill considering his future in west London.
Tuchel will hope to strike a deal for at least one more defender before the Premier League campaign gets under way next weekend.
"We are looking for guys who can play on the left side," Tuchel told Chelsea's official website when asked about his centre-back search.
"Toni [Rudiger] played on the left side and was not a left-footed guy, so maybe Kalidou can play there because he plays in a back-four on the left side, but let’s see what is possible.
"It is not only about bringing players in for numbers; we need numbers, we also need quality so we will make some decisions late, not only about players but also about systems. Ideally we would have a left-footer."
