Suspended duo Verratti and Ibrahimovic missed PSG's 3-1 loss to Barca in their quarter-final first leg last week but are set to reinforce the capital club in Catalonia on Tuesday.
Ibrahimovic's position at PSG has been questioned over the past month after the Swedish striker was banned for an expletive-laden rant against Ligue 1 referees in March, but Verratti insists the 33-year-old is a calming influence on the team.
"I'd like to talk to you about what Zlatan is like behind closed doors, because everyone knows what he's like on the pitch," Verratti told PSG's own television show This is Paris.
"But it's away from it where he plays such an essential role. He's always on hand to help his teammates and he exerts so much confidence in the team. He helps the young players progress. He's there for everyone really.
"He always speaks his mind. And no matter what he says you have to listen to him because he has such great experience. He's such a great player and it's such a privilege to be given the opportunity to play alongside him."
Ibrahimovic last played for PSG in their 4-0 demolition of Bastia in the Coupe de la Ligue final on April 11 where he scored twice.
That was also Verratti's last appearance, with the Italian midfielder having played in six of PSG's nine Champions League matches this season.
PSG are aiming to reach the Champions League's final-four for the first time since 1994-95.
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