Chelsea centre-back Trevoh Chalobah is believed to have reinjured his hamstring in Sunday's 2-2 draw with Liverpool.
The academy graduate, who has been nursing the issue since early December, looked uncomfortable against Liverpool and was guilty of a poor header which allowed Sadio Mane to open the scoring in the first half.
Chalobah was substituted off after 70 minutes and looked in some discomfort as he left the pitch, and Adam Newson has revealed that there are concerns over the defender's hamstring once again.
The belief is that Chalobah was actually a doubt for the game because of this injury, but the decision was made to risk his fitness and it does not appear to have paid off.
Thomas Tuchel is already without Denmark international Andreas Christensen, who has a back injury, while the hamstring tear suffered by right-back Reece James has seen Cesar Azpilicueta used out wide rather than at centre-back.
Frenchman Malang Sarr was Chelsea's only centre-back on the bench against Liverpool and he can expect to play significant minutes in the first leg of the Carabao Cup semi-final against Tottenham on Wednesday.
Tuchel is yet to give any minutes to academy centre-backs this season but has welcomed at least three to training in recent weeks.
Dutchman Xavier Mbuyamba joined Alfie Gilchrist and Josh Brooking in training ahead of the quarter-final against Brentford, and with Tuchel so desperate to manage the minutes of his senior stars, he may do the same again here.
Forward Harvey Vale and versatile midfielder Lewis Hall, who has played some minutes at left wing-back for the academy sides, were both on the bench against Liverpool and will hope to see some game time on Wednesday.