Tuchel seems to have no more hope for Mane after seeing the game he gave last season.
We ourselves also know that Mane doesn't provide many good developments and he doesn't even look very enthusiastic in every game he plays.
Mane was injured a lot last season, he is still a good player but Tuchel and Bayern munich don't want a player that is above 30 and is findng it hard to be fit. Mane also had a serious problem with Sane last season as the two players fought in the dressing room, all these things makes it hard for Mane to continue playing for Bayern munich.
When Mane came to the bundesliga, we thought he was going to be an important player for Bayern munich, though he won the bundesliga with them, but he didn't contribute much to it. Mane is going to go to Saudi Arabia, and that may be the best choice for him.