Neymar, 28, has not played since the start of February and Tuchel has preserved him since he took a knock to his ribs during a home league win over Montpellier.
“Neymar is fine — as long as nothing happens in training, he will play on Tuesday,” said Tuchel. “His return changes almost everything for us. Positively, I hope.
“We have quality if Neymar is on the pitch. He has the ability to do decisive things. It changes everything for us — it gives the team confidence. We do not have many other players of the same calibre.”
For Tuchel, it is a return to his former club in Germany and the 46-year-old recognised that he and his squad face a tough task at Westfalenstadion.
“Returning to Dortmund is a great challenge,” he said. “It will not be me — we will have to show a strong face here.”
Asked if PSG need to avoid being drawn in by the emotion of the occasion in the Champions League, Tuchel pointed to Manchester City boss Pep Guardiola’s example and wants to see intelligent play from his team.
“Pep knows all about it as he has won it three times — he is right,” he said. “It is difficult to control emotions at this stage — I do not know if it is even possible.
“We have to play with intelligence, not so much emotion. We need to adapt and fight. It is a great fixture, in a great stadium that will be full of incredible supporters.
“The atmosphere here is special. It is not possible to prepare for a match like this in just two days. I feel we are ready.”
Tuchel admitted that he was “mentally dead” after last season’s unexpected elimination at the hands of Manchester United.
“Right after United, I told the team that we would bounce back — that we would have the chance to recover,” he said. “I died mentally after that match. It is sport, you have to adapt and bounce back.
“It is the competition and we are still here. This is a tough task, but we cannot control the result — only ourselves. We have to enjoy ourselves, fight, and win against Dortmund. In the end, the result has to be accepted.
“If you fall three times in the round of 16, the fourth is not the same situation. Each year has its own story. There are more important professions than this. Sometimes you happen to lose, even if you want to avoid it. You have to learn from losses, grow and develop.”
On top of Neymar and Mbappe, Presnel Kimpembe is also back after missing last Saturday’s trip to Amiens.