Matt Miazga is set to join Anderlecht on a season-long loan, the United States centre back's fourth temporary move since joining Chelsea in January 2016.
The 25-year-old had not been given a squad number and was not part of the club's testing bubble - meaning another loan was always on the cards.
He has made two Premier League appearances for the West London side, both at the end of the 2015-16 campaign, and spent last season as a regular for Reading, following on from spells at Nantes and a two-year move to Vitesse.
The former New York Red Bull, who cost Chelsea about £3.5million, had received interest from a number of clubs, including in the Sky Bet Championship and Scottish Premiership, but has opted to join Vincent Kompany's side.
Confirmation of the deal is expected imminently.
Miazga is the 23rd Chelsea player to head out on loan this season and that number could rise to about 30 by the close of the transfer window.
A number of players with squad numbers but unlikely to be regulars under Frank Lampard this season are expected to head out on loan, including Ruben Loftus-Cheek and Toni Rudiger, while there are four goalkeepers on the books.
One from Kepa Arrizabalga and Nathan Baxter, who has been reduced to fourth choice since Edouard Mendy's arrival from Rennes last week, will likely leave before Monday night.
Several other players deemed surplus to requirements are searching for moves, including midfielders Danny Drinkwater and Tiemoue Bakayoko, wing back Victor Moses and defender Jake Clarke-Salter.
