Christensen is sidelined with a muscle issue, while Kovacic sustained a hamstring problem before the second leg of their Champions League quarter-final with Porto and is out of contention for this game, so N'Golo Kante and Jorginho are set to man the engine room.
The Chelsea boss has no selection concerns otherwise, but he must decide whether to keep faith with Edouard Mendy in goal or recall Kepa Arrizabalaga, and the Spaniard will hope to continue his FA Cup run here.
Cesar Azpilicueta and Antonio Rudiger will both be eyeing starts in defence, but 36-year-old Thiago Silva has missed out several matches recently due to injuries and suspension, so Kurt Zouma could earn a place at the back as Tuchel looks to keep Silva fresh.
Reece James is expected to keep his place on the right over Callum Hudson-Odoi, but Marcos Alonso has plenty of experience playing at Wembley, so he could be rotated in for Ben Chilwell on the opposite side.
Mason Mount is undroppable at the moment, but Christian Pulisic is another player that Tuchel needs to be careful over given his recent fitness woes, so Timo Werner is a candidate to start over the American, who played the full 90 in midweek.
Tammy Abraham sits atop the FA Cup goalscoring charts with four strikes to his name, but the Englishman has fallen out of favour at Stamford Bridge, and Kai Havertz finally appears to be hitting his stride after a tough start to life in London.
Chelsea possible starting lineup:
Kepa; Azpilicueta, Silva, Rudiger; James, Jorginho, Kante, Alonso; Mount, Werner; Havertz