Tuchel has kept faith with Werner after his glaring miss in the first leg in Spain last week.
The only question is whether Havertz or Werner will be leading the line.
Cesar Azpilicueta starts at right wing-back and the rest of the team is as expected.
Toni Rudiger starts and will wear a protective mask after suffering a facial injury in the first leg. He forms a back three with Thiago Silva and Andreas Christensen.
Chelsea XI: Mendy; Christensen, Silva, Rudiger; Azpilicueta, Kante, Jorginho, Chilwell; Werner, Mount; Havertz.
Subs: Kepa, Caballero, Alonso, Abraham, Pulisic, Zouma, Giroud, Hudson-Odoi, Ziyech, Gilmour, James, Emerson.