Tuchel's men, who lost in last season's final to Bayern Munich, face a challenge to progress to the last 16 of this year's competition after a series of unconvincing performances in the group stage.
United, having won the reverse fixture in Paris, leads Group H with nine points, with PSG and RB Leipzig level on six points heading into the final two pool games.
Key to PSG's struggles has been their form in front of goal. While United have scored 12 goals in four games, PSG have found the net just five times.
United has converted 21.8 per cent of their shots compared to 10.4 for PSG.
PSG has taken advantage of 37.5 per cent of their big chances. In stark contrast to the profligacy shown by the Ligue 1 champion, United has found the net from 83.3 per cent of its big chances.
Mbappe has not scored in the Champions League since a 5-0 win over Galatasaray on December 11 last year, despite taking 11 shots - including one big chance - this term.
Of that barren run, Tuchel said: "I heard about that statistic [the drought] and I was surprised.
"I can't explain it because he has everything needed to score at every level. He has the quality, the personality and the experience to be decisive."
Marcus Rashford has been the match-winner for United in each of the past two meetings between United and PSG, famously knocking them out in the last 16 of the 2018-19 competition.
Asked about impressions of the England forward outside of his home country, Tuchel said: "We value him also when he plays in England, not in Parc des Princes because this gets a little bit annoying.
"The guy is a very young adult who takes his responsibility off the pitch very impressively. I met him three times as an opponent; every time I meet a calm guy, a humble guy, a nice person. I like this kind of mixture a lot.
"The sporting side is clear, he's a big threat with his speed, with his precision and his finishing, his determination. He is super rapid on counter-attacks, strong in the air for headers. It's nice to see guys like him from the academy making such a big impact."