Italy international Verratti came back from a knee injury in the 2-2 draw against Real Madrid on November 26, but a thigh issue sustained in training later that week resulted in a return to the treatment room.
Despite PSG being granted a matchday off when rain forced the postponement of their Ligue 1 meeting with Monaco on Sunday, the 27-year-old remains sidelined with fellow midfielder Ander Herrera, who has not played for a month due to a hamstring problem.
"Marco Verratti and Ander Herrera are injured and Presnel Kimpembe is suspended. All the others are fit," said Tuchel.
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"Not playing on Sunday was a surprise. We had prepared the game, announced the starting 11 to the players, had a tactical meeting and then the game was postponed.
"I had an idea for Monaco, and a different one for Nantes. But without playing Sunday's game, it makes a difference. We've adapted. We took the return flight and then trained on Monday. I am convinced that we will be ready on Wednesday.
"We are expecting Nantes in a 4-4-2. They started the season well, with many good results. It has been more difficult in recent weeks, but they won their last game. They're a very strong team, defending together. So it will be a tough game for us, but I think we're ready."
PSG captain Thiago Silva will be out of contract at the Parc des Princes at the end of the season and Tuchel was unable to offer an update on the Brazilian's future.
"It is not my decision. It is something between the player, his agent and the club. The coach just gives their opinion," Tuchel said.
"We have to wait, to be patient. We prefer to talk about it if we have something to say. Thiago Silva is our captain. There is nothing new about this."