The Croatian midfielder was not fit enough to face off against his old club Real Madrid in the Champions League in midweek, and having suffered a small setback in his recovery, Saturday's game will come too soon for him as well.
Thomas Tuchel surprisingly benched Christian Pulisic for the second leg, but the American winger set up Mount for the game's second goal and will hope to earn a recall here, meaning that Timo Werner's spot is in jeopardy despite his opener on Wednesday.
Cesar Azpilicueta and Ben Chilwell could both be given a rest after playing their part in a clean sheet against Los Blancos, which would give Reece James and Marcos Alonso the opportunity to bomb down the flanks.
Thiago Silva continues to marshal the Chelsea backline admirably, but Tuchel may want to be cautious over the 36-year-old's fitness amid an intense schedule, so Kurt Zouma is in contention to start over Silva this weekend.
Chelsea possible starting lineup:
Mendy; Zouma, Rudiger, Christensen; James, Jorginho, Kante, Alonso; Mount, Pulisic; Havertz
Watch the Sports Mole Football Shorts prediction for this game below: