The teenager is set for a second stint in the Championship with Billy Davies's side after spending last season at Vicarage Road with Watford
The 18-year-old moves to the City Ground until January 15 and could make his debut for Billy Davies’s men on Saturday against Doncaster.
The England Under-21 international signed a five-year deal with the Blues in August but has yet to make a first-team appearance for Chelsea.
Chalobah spent last season on loan at Watford, helping Gianfranco Zola’s men reach the play-off final where they lost narrowly to Crystal Palace.
The teenager, who can play in defence or midfield, is a regular in the England Under-21 side and played in this summer’s European Championships.