Kovacic had to be withdrawn after just 30 minutes as he could not carry on after taking a blow to his ankle after a reckless tackle from Dan James, who was shown a straight red card.
Tuchel confirmed the ankle was swollen and the Croatian in “a lot of pain” after Chelsea‘s 3-0 win, the Blues’ first victory in four games, with Kovacic now needing “a miracle” to feature at Wembley.
“I tell you not as a coach, not as an expert but I think it’s very unlikely we see him [in the FA Cup final],” Tuchel told reporters.
Once Mateo goes out, he never goes out, he played in the semi-final of the FA Cup with the same injury and tried to play another 15 minutes, which is almost impossible.
“He has a swollen ankle and is in a lot of pain. I’m not a doctor and we need to wait for the examinations, but it’s very unlikely. It’s absolutely bad news on a perfect evening.
“If he misses it, I’m very disappointed because he was a clear starter,” Tuchel continued. “If you look at the quality with him and Jorgi [Jorginho] in the centre of midfield when it was 11 against 11.
“It was a strong start and he is a key figure for us. He played against Liverpool in both of the last matches from the beginning, if I remember right, and was always very strong.
He’s super, super hungry, determined and excited to play these matches. He’s in fear now that he will miss it, we will see. Maybe we have a miracle and it will be possible.”
Along with Kovacic, Chelsea are also sweating on the return of N’Golo Kante, who has missed their last three games due to injury – leaving a number of midfield unknowns for both sides at Wembley.