Tuchel revealed he spoke with Grealish to explain his reasons, while admitting the midfielder's highly-publicised boozy nights out aren't helping him.
"I love Jack," Tuchel said on Friday. "As a headline, I love Jack. I love everything about him. I love his personality, I love his quality.
"The guy has courage, he can take the heat, he's not afraid of the Bernabeu whistles when he's on the ball, it does not affect him and if it affects him only in the best way. So is he a player that should be available and can have an impact in our squad? Yes, 100 per cent.
"But lately, he simply has no rhythm and he himself and I agree 100 per cent with this. he said, 'Listen Thomas, I'm not a start-stop player. It is so hard for me to influence a match from the bench and then be on the bench again, and then two weeks later I start again'."
Tuchel also stated: "The more he plays the better he gets and then he becomes a proper machine.
"And he has, of course, a character to him that he can be the glue also in the team.
"It's very easy for youngsters and for experienced players to be attached to him and to be close to him.
"But this comes also with responsibility off the pitch and, of course, it's not ideal that he's in the newspapers and out there in public. But it was a sporting choice and in his position Anthony Gordon is just more rhythm, more minutes."