The 36-year-old Brazil defender is almost ready to return after a thigh injury, but boss Thomas Tuchel will not rush him back into action.
Sheffield United's David McGoldrick could return to action in the tie.
The forward, who missed the 5-0 loss at Leicester last weekend due to a knee injury, trained on Friday and was being assessed.
Chelsea provisional squad: Mendy, Azpilicueta, Zouma, Rudiger, Hudson-Odoi, Chilwell, Kante, Jorginho, Mount, Havertz, Ziyech, Giroud, Arrizabalaga, James, Christensen, Emerson, Alonso, Kovacic, Gilmour, Pulisic, Werner, Abraham, Anjorin.
Sheffield United provisional squad: Ramsdale, Foderingham, Baldock, Stevens, Basham, Lowe, Jagielka, Bryan, Bogle, Ampadu, Bryan, Fleck, Lundstram, Norwood, Osborn, Ndiaye, McBurnie, Sharp, Mousset, Burke, McGoldrick, Brewster.