Chelsea are in talks to sign Napoli defender Kalidou Koulibaly and Manchester City centre-back Nathan Ake.
Thomas Tuchel's side have been left short in central defence after the departures of Antonio Rudiger to Real Madrid and Andreas Christensen to Barcelona, both on free transfers.
The Blues are hopeful of signing both Ake and Koulibaly.
Meanwhile, Raheem Sterling's move from Manchester City is expected to be confirmed in the next 48 hours.
The England forward is flying out to join the Chelsea squad in Los Angeles before his transfer from City is completed.
The 27-year-old has agreed a five-year contract to join Tuchel's side in a £50m deal.