The 26-year-old pulled out of last weekend's FA Cup Final against Liverpool just hours before kick-off with Tuchel hinting at issues that have restricted the centre-back's availability for several weeks.
Christensen has started just one of the club's previous six matches -- a 3-0 win away at Leeds on May 11 -- as he closes in on a move to Barcelona this summer when his contract at Stamford Bridge expires.
"I don't think it is that he does not want to play, he was not able to play [against Liverpool]," Tuchel said. "It is a huge difference. We had more than this conversation but on the Saturday morning, he finally told me.
"[I am] not sure yet if he is involved [on Thursday] and on the weekend but Andreas came on the morning of the [FA Cup final] to inform me that he is not ready to play, not to start and not be on the bench.
"He had his reasons, they stay private and confidential. It was not the first time as you can see over the last weeks that we had some of the same situations.
"That's why he did not play so regularly over the last weeks. We thought that we are in a good progression, in a good development because he played very, very strong in the match before the final against Leeds.
"The conversation took place, we had to respect it, we of course respected it. He still has our support but for tomorrow I'm not sure. Probably unlikely for the weekend. It was on very short notice before the cup final and not only before this match, in other matches in the weeks before so no chance I have any prediction it will be [Thursday] or the weekend."
Asked whether he felt let down by Christensen, who joined Chelsea from Brondby aged 15 in 2012, Tuchel said: "We had to accept it and we will accept it. I try the best I can not to take things personal and I still believe Andreas wanted to play in these kind of matches.
"I still believe that he could in terms of potential and what he gives to the team. That's why he was a key player for us but he struggled over the last few weeks when he was not in the squad or not playing.
"Also he was physically available, not being injured physically. So that was not completely out of the blue sky. I am missing maybe the word here, it was not the ideal scenario for us. We thought we prepared him in the best way possible and with the game at Leeds, where we managed a lot of pressure on us in a very impressive way, we thought we had him available.
"He is a key player and if you arrive in a final against Liverpool, you want all your players available which is not the case."