Chelsea manager Enzo Maresca has made several changes to the starting XI that defeated Palmeiras in the quarter-final of the Club World Cup.
Tosin Adarabioyo comes in to form a central defensive partnership with Trevoh Chalobah, with Liam Delap and Levi Colwill both suspended.
Maresca also starts João Pedro ahead of Nicolas Jackson following his £60 million move from Brighton.
Moisés Caicedo replaces Andrey Santos in midfield, while Noni Madueke drops to the bench amid transfer links to Arsenal.
The winner of this semi-final will face either Real Madrid or Paris Saint-Germain in the final.
Chelsea XI:
Team to play Fluminense: Sánchez; Gusto, Tosin, Chalobah, Cucurella; Caicedo, Fernández; Pedro Neto, Palmer, Nkunku, João Pedro
Fluminense XI:
Team to play Chelsea: Fábio; Da Silva Oliveira, Thiago Silva, Dos Santos; Guga, Hércules, Bernal, Nonato, Rodrigues; Arias, Cano
