The Spanish club have made an initial offer of €4.5m, although that is currently short of what the Blues are asking for for the defender
Leganes have made a €4.5 million offer for Chelsea defender Kenneth Omeruo, who impressed during a loan spell with the Spanish club last season.
The Blues are, however, holding out for €7m (£6m/$8m), with Celta Vigo having previously been interested prior to their signings of Joseph Aidoo from Genk and Jorge Saenz on loan from Valencia.
The 25-year-old is keen to depart Stamford Bridge and he has been spending his summer at the Africa Cup of Nations with Nigeria.
Former Southampton manager Mauricio Pellegrino built up a strong rapport with the centre-back at Leganes last season and is hoping to have him back for the 2019-20 campaign.
West Ham and Brighton are reportedly targeting Youssef En-Nesyri from the Liga club, which could help raise further funds for a deal for the Nigerian.
En-Nesyri is Leganes’s record signing at €6m (£5m/$6.5m) and the Madrid club are hopeful that they will not have to surpass that figure to sign Omeruo.