The Frenchman had been out since suffering an ankle injury in the Coupe de France final win over Saint-Etienne on July 24, but managed to feature off the bench in the quarter-final of the Champions League against Atalanta, and helped to change the game in favour of the Ligue 1 champions.
With a third of the game remaining against Atalanta, Mbappe entered the action with PSG 1-0 down.
It took until the 90th minute, but the French side eventually pulled one back to make it 1-1 before Mbappe assisted the dramatic winning goal a couple of minutes later in injury time.
Even though he was unable to start that match, he looked sharp when he entered proceedings, and Tuchel has confirmed that he expects Mbappe to be in the starting XI versus RB Leipzig.
"He played for 30 minutes against Atalanta and had no reaction and had six days since to work on fitness, so of course he can start," the former Dortmund boss said on Tuesday.
"We will decide after training whether he can play 90 minutes."
The victory against Atalanta allowed PSG to reach their first Champions League semi-final in 25 years.