Chelsea are set to sign Senegal international Papy Djilobodji from Nantes in a £4m deal.
The defender is due for a medical after agreement was reached between the clubs for the transfer of the 26-year-old.
Chelsea boss Jose Mourinho has turned his attention to the 6ft 4in centre-back after failing to sign England's John Stones from Everton.
Winger Victor Moses, 24, is expected to sign a new contract at Stamford Bridge before joining West Ham on loan.
Djilobodji, who is in the last year of his contract, has made more than 160 appearances for Nantes since joining the French club in 2010.
Mourinho has moved to address the Premier League champions' defensive concerns after they conceded nine goals in their first four league games.
That has left them eight points behind leaders Manchester City before they return to action at Everton on 12 September.
Nigeria international Moses, who has two years left on his current deal, is set to join the Hammers on a season-long loan.
He has spent the last two seasons on loan at Liverpool and Stoke after joining Chelsea from Wigan for £9m in 2012.
