Mateo Kovacic has tested positive for Covid-19 which has ruled him out of Chelsea's clash against Zenit St Petersburg on Wednesday night in the Champions League.
After returning to training this week following a hamstring injury that has kept him out since the end of October, Kovacic was set to return this weekend against Leeds United.
He was missing from training on Tuesday morning ahead of the trip to Russia to face Zenit, which was thought to be injury/fitness related.
But Tuchel offered a major setback for the Croatian, confirming he had tested positive for Covid-19 and will now need to self-isolate.
“We have bad news," said Tuchel in his pre-match press conference. "Mateo was in training yesterday with a big smile and a pure pleasure to have him back. He got tested positive today for Corona so he is isolating. Current headache. He is out for another several days, a huge setback for him personally and for all of us.”
Chelsea also have central midfield duo N'Golo Kante (knee) and Jorginho (back) out of the European clash as the Blues eye top spot in Group H.
It's a concerning time for Tuchel and the Blues regarding injuries with Trevoh Chalobah and Ben Chilwell also sidelined.
It's given plenty for Tuchel to ponder in terms of team selection which could see Ruben Loftus-Cheek and Saul Niguez both start at the Gazprom Arena.
The Chelsea head coach did confirm changes will be made on Wednesday night.
He added: "Long story short, there is a huge chance we rest some players. Maybe more important, we give some players who need the load and the minutes, to give them rhythm. The decisions will be made tomorrow, there’s a huge chance for that.”