The 20-year-old defender and midfielder Jason Mount are on a season-long loan deal with the Championship side, under the tutelage of Blues legend Frank Lampard.
The duo have been crucial to the plan of the former England midfielder since arriving the club in the summer. Also, they played stellar roles in the third round upset against Manchester United at Old Trafford.
In the fourth round, they face Maurizio Sarri's side and, unlike Premier League rules that do not allow loanees to feature against their parent clubs, the EFL Cup allow for such agreements, given there is a written consent.
Goal understood that Chelsea kicked against having two of their brightest youth prospects play against them but, on Monday, agreed to have them participate in the encounter which they believe will benefit their ongoing developments.
“Mount and Tomori have been regulars for the Rams under Frank Lampard this season, and, after beating Manchester United at Old Trafford in the previous round, we believe the experience of facing top-level opposition once more will be of benefit to their on-going development at Derby,” read a statement on Chelsea website.
Tomori has played in 12 English Championship encounters, helping Derby to fifth place in the log and has league games against West Bromwich Albion and Middlesbrough to prepare for before next Wednesday's trip to Stamford Bridge.