Chelsea are in talks over a deal to sign the Napoli centre-back Kalidou Koulibaly as Thomas Tuchel pushes to fix his side’s defensive crisis before the start of the Premier League season.

The departures of Andreas Christensen and Antonio Rüdiger have left a huge hole in Tuchel’s defence and Chelsea’s head coach would like to sign at least two centre-backs. Personal terms have been agreed with Nathan Aké, who will cost at least £40m, and the spending will not stop if the Manchester City centre-back completes a return to Stamford Bridge.

Chelsea, who could secure the signing of Aké this week, have several defensive targets. They remain interested in Sevilla’s Jules Koundé and, with Bayern Munich leading the race for Juventus’s Matthijs de Ligt, Koulibaly is emerging as a viable option for Tuchel. Sources have suggested an agreement over a £34m deal for the Senegal international is not far away.

Koulibaly has impressed since joining Napoli in 2014 and is regarded as one of the best defenders in Serie A. The 31-year-old remains in good shape and is seen by Tuchel as a player who could slot into his defence straight away. Napoli have offered Koulibaly an extension to his contract, which expires next year, but are aware that Chelsea can offer him more money.