PSG and United meet first in Manchester on February 12, with the second leg taking place in the French capital on March 6.
United beat another Champions League side, Tottenham, at the weekend to record their six successive victory under caretaker manager Ole Gunnar Solskjaer, a run of results that has made PSG sit up and take notice.
“I think after the departure of Jose Mourinho Manchester United has a new energy,” said striker Edinson Cavani, speaking at French champions’ winter training camp in Doha, Qatar.
“They have started to win matches and have more continuity.”
He added that three-times winners of the European Cup/Champions League were “a strong group”.
When the draw was made, many made PSG clear favourites to win the tie with an uninspired United well off-the-pace in the Premier League title race.
But they are a team transformed since Solskjaer replaced the sacked Jose Mourinho in December, with a revival capped off by this weekend’s impressive victory away at Spurs that has them closing in on the European spots after falling way behind.
Central to that transformation has been World Cup winner Paul Pogba and his France teammate Kylian Mbappe said United had a “strong squad”.
“I think Manchester United is always a top side,” said Mbappe.
“It’s not easy to play any team in the Champions League, we are going to do our best.”