The Daily Telegraph are reporting that the Blues have submitted a £60m bid for the Senegal international as Antonio Conte looks to bolster his defensive options at Stamford Bridge.
The same article states that the west London side are willing to go as high as £60m in an effort to force the Naples outfit to sell their prized asset this summer.
Chelsea’s current transfer record is the £50m purchase of World Cup winner Fernando Torres from Liverpool in 2011.
Conte was appointed as the next Chelsea permanent manager earlier this year and the Italian took over the reins after Euro 2016 this summer.
The former Juventus defender signed Belgium striker Michy Batshuayi in a £33m deal from Ligue 1 side Marseille at the start of July.
Conte has since added Leicester City’s title-winning midfielder N’Golo Kante to his squad in a £30m deal.
Chelsea made a winning start to life under Conte in the Premier League on Monday after a 2-1 victory over West Ham United in their first London derby of the season at Stamford Bridge.
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