The Ligue 1 champions host Ole Gunnar Solskjaer's men at Parc des Princes for the first time since the Red Devils ran out 3-1 winners to seal a place in the quarter-finals of the competition in March 2019.
Despite a recent 6-1 loss at home to Tottenham, United have won four of their last five games in all competitions and are coming off the back of a 4-1 win at Newcastle.
Tuchel feels his side will have to pay close attention to the Red Devils' midfield and work hard to suppress Paul Pogba and Bruno Fernandes if they are to start their European campaign with a win.
"Pogba remains a key player who, with his talent, is one of the best midfielders in the world," he told reporters. "It is clear that we have to stop him, like Bruno Fernandes who makes a lot of assists.
"Pogba and Bruno Fernandes are key players in the middle. With Nemanja Matic, they're very strong. They play with super-fast attackers, and for me they are one of the strongest teams in Europe in the attacking transitions.
"It will be necessary to stop them before the counterattacks. We want to take the ball, show our style and impose it, but we need to play with a good structure to evolve with a good counter-pressing and to prevent opposing counter-attacks, especially since they are also efficient on set pieces.
"These are key points on which it will be necessary to defend well."
PSG reached the final of the competition last term and are looking to go all the way again this year, but Tuchel says he is not sure if they are even stronger this season.
"Honestly, I don't know [if we're better]. We have to prove and it's difficult because we had a super strong team last season," he added. "But it's sport. A new competition begins and we have to show the same.
"The question is not whether we are more or less strong. Last season's Champions League is over. We have to show what we are worth today, and it is only after the season that we will be able to answer this question."