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.
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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.