"Set-pieces will be a key of the match though not the only one," Blanc told a news conference on Monday.
"They have a very athletic team. I think we lack a bit of height. We will not be able to fight them in the air because PSG players won't grow 10 centimetres taller overnight," he added.
"So if we don't control the game, if we don't force them to adapt to our play, their philosophy will prevail, with fast counter-attacks and set-pieces. And we are going to suffer."
Leverkusen often threaten their opponents on free kicks or corners but they also concede a lot of goals in the same way.
"This is a paradox but it means that they are better in those kind of situations when they attack. We'll have to keep that in mind," Blanc said.
In the absence of Edinson Cavani, Blanc will be looking to striker Zlatan Ibrahimovic to produce a top European performance.
Ibrahimovic was rarely decisive in the knock-out stages with his prestigious former sides Juventus, AC Milan, Inter or Barcelona and he has never won the competition.
But Blanc said he had no doubt the Swede, who has enjoyed his best Champions League campaign so far with eight goals in the group stage, will live up to expectations.
"He's going to turn 32 this year, he's more mature and he has a lot of experience," Blanc said.
"He scores goals, he has always scored and he will continue to score until the end of his career. He will be our main asset because he's the one who scores the most in this team."
"I think that Bayer will focus on him and that he will come out in force. He loves the big games, he's more motivated and, hopefully, he will be more efficient than he is in the (French) league."
PSG will host the return leg at Parc des Princes on March 12.
(Writing by Gregory Blachier in Paris; Editing by Clare Lovell)
