Kovacic suffered an ankle injury after a lunging tackle that saw Dan James dismissed in Chelsea's 3-0 Premier League win over Leeds United on Thursday (AEST).
Tuchel, speaking after the game, expressed his concerns over a "major injury" to the Croatia international on an otherwise "close to perfect evening".
However, Chelsea manager Tuchel provided a positive update on Kovacic as he revealed the midfielder had been given the green light to train by the medical team.
"We will try it today, which is pretty surprising news where we can even try it but Mateo wants to and the medical department gave the green light," he said ahead of the Cup final.
"The advantage is there is no new injury, the ligament was already torn from the last injury, but heavy pain, heavily swollen.
"So we're hoping that maybe time is enough that he makes it, we will try it in two-and-a-half hours in training and see. In the game [at Leeds], he was very, very good, in general, he has stepped up.
"The qualities of him and the personality, his dribbling and driving with the ball is excellent and he's a top team player.
"He played many years for Real Madrid so knows what it takes to put the ego aside and serve the team.
"We have missed him too much this season, with injuries over the season, and he is now so ambitious before the FA Cup final because he was excellent against Liverpool recently."
Tuchel also hopes to have N'Golo Kante back after the France international has missed the past three games, last featuring against Manchester United on 29 April (AEST).
"It was a reduced training session because of a long journey and fatigue of travelling. We will also try today with him. He is keen to make it and hopefully he makes it to training 100 per cent," the German said of Kante.
Sunday (AEST) will be just the second time the same two sides will contest both the Carabao Cup and FA Cup final in the same campaign.
Jurgen Klopp's Reds were penalty shootout victors in February and all three games in 90 minutes have finished level between the two teams this season.
The previous fixture between two English top-flight sides to see more stalemates in the same campaign was Arsenal versus Chelsea in 2017-2018 (four), and Tuchel expects the final to follow a similar pattern.
"It started with last season's game at Anfield, this season's draw at Anfield, a draw at Stamford Bridge, and then over 120 minutes and the penalties [in the Carabao Cup final]," he added.
"I don't expect crazy new things from them and also not from us."
Chelsea is the first side to reach three consecutive FA Cup finals since Arsenal between 2000-2001 and 2002-2003.
However, after losing in both 2019-2020 against Arsenal) and 2020-2021 against Leicester City, it is looking to avoid three such final defeats since Newcastle United in 1998-1999 and Tuchel believes an element of luck will be required.
"It's a big achievement to be in the finals and there has to be a loser in these finals," he said. "There is a special momentum you have to catch and a bit of luck.
"The atmosphere is right and the momentum is okay after the reaction at Leeds and everyone knows what we're up to. We want to arrive to give Liverpool a hard fight."
As for whether Kepa Arrizabalaga, who missed the decisive spot-kick in the Carabao Cup final after being substituted on specifically for penalties, will be utilised in extra-time again, Tuchel insists he has a plan.
"It's never done before and it's not done now. We have a plan for it. What we can do in terms of practising, I'm a bit torn about how much you can practice it," Tuchel continued.
"My players shoot a lot of penalties on a daily basis through the season, which in my opinion is good to have a certain routine for the players.
"But to shoot tomorrow after 120 minutes of intense fight and in a full stadium, it's a different story."