Cavani has only started four Ligue 1 fixtures this season and five across all competitions in 2019-20.
Asked about the Uruguay international, Tuchel told reporters: "I spoke with him. We both know it's very difficult for him. It's not only a difficult decision for me, it's also sad.
"We played a lot of games with three strikers including one number nine. Cavani was injured at the beginning of the season, it's not his fault. Mauro [Icardi] played very well during that period, he scored a lot.
"If we play in 4-3-3, we have three extraordinary players for a position in front [as number nine], Kylian [Mbappe], Mauro and him. I'm sad because I don't have a solution [to include him in the line-up] right now.
"He doesn't deserve that, he's very professional, in a good state of mind in the locker room, he gives a good energy to the team. But right now I don't have much playing time to give him."
Cavani, who arrived from Napoli in 2013-14, has scored twice for Tuchel's French champions this term.