Chelsea defender Malang Sarr was undergoing a medical with Monaco on Monday ahead of completing his loan move.
Monaco are paying around £650,000 for the loan fee with a £10m deal agreed to make the move permanent next summer plus a further £3m in bonuses.
Sarr, 23, also had an offer from Fulham but was keen to return to France with Monaco.
He made 21 appearances for Chelsea last season and has previously been on loan at Porto.
Chelsea are also waiting on Barcelona finalising a deal for Marcos Alonso while Timo Werner is rejoining Red Bull Leipzig.