Chelsea will not allow Frank Lampard permission to select loanees Mason Mount and Fikayo Tomori for Derby's trip to Stamford Bridge in the fourth round of the Carabao Cup, Goal understands.
The Blues legend returns to the capital as manager of the Championship club in what will be a special occasion for him personally, having spent 13 years of his playing career in west London.
Lampard's Chelsea connection will no doubt have helped him seal loan deals for the pair, two of the London club's brightest academy products, but EFL rules restrict the use of loanees against parent clubs without written consent.
Chelsea have declined use of loanees against them by Championship clubs in the past, with Hull City being denied when they were beaten 4-0 in the FA Cup by the Blues last season.
Hull had Tomori on loan at the club, as well as Michael Hector and Ola Aina ineligible to play at Stamford Bridge, which left them short in defensive positions. This situation was slightly different, however, as FA rules prohibit their use, while EFL ones leave the doors open for the clubs to decide.
The EFL rules state that "players registered on a temporary basis will not be eligible to play unless the Club holding his full registration gives written consent (also subject to any restrictions on the number of loan players prescribed by applicable Premier League rules or League Regulations)".
Mount has been pivotal for Derby so far this season, netting five goals and getting an assist from midfield, while he scored his penalty as Lampard's side knocked Manchester United out of the cup by winning 8-7 on penalties after a 2-2 draw in normal time.
Tomori has also been impressive for the Rams this season, playing 11 times as a centre-back for the team that sit eighth in the Championship table.
Derby's Chelsea connection runs deeper than Lampard, too, with Under-18s boss Jody Morris and first-team coach Chris Jones arriving from the west Londoners over the summer.
