The Blaugrana playmaker believes the Argentina international is needed if the club is to win trophies, however, he is confident the team can overcome PSG without him.
The Argentina international picked up a hamstring injury in the first leg of the Champions League quarterfinal against PSG shortly after he put the Catalans ahead and is a doubt to play in the second leg with the score finely poised at 2-2.
"We will see today [Tuesday] and tomorrow if Leo Messi can play. It all depends on how he feels. They will decide if he can play or not,” Iniesta said during a press conference. “He sustained an injury so they need to talk to take a decision.
"Without a doubt, there is Messi dependence in the team in the sense that he's a fundamental player, but then there's no Messi dependence because we're a team and lots of players can score goals. We need to reach June with all the options to win titles. Leo is a fundamental and decisive player for us. He's the No.1.”
Meanwhile, Iniesta also hailed the impact of Cesc Fabregas, who netted his first hat trick of his career in the 5-0 demolition of Mallorca on Saturday.
"I am lucky enough to have such a complete player alongside me as Cesc," he continued. "He helps my game and the team's performance. He interprets exactly where his teammates are on the pitch and that's fundamental.
"He interprets our game perfectly well. He played at a very high level when he left the club and now we are fortunate enough to have him back here. I hope he carries on playing as well as he is until the end of the season and he helps us win titles."
The 28-year-old is not underestimating the threat Paris Saint-Germain carries. but insists if Barca plays to its best then the Spanish club should win.
"PSG are very fast when it comes to reaching our penalty area," he said. "They have technically very good players, a very complete squad with a lot of talent.
"We have to take all that into account, but we just have to do our job. If we play well, the opposition will suffer and we will have a good chance of winning the match."
Long-term absentee Eric Abidal made his comeback at the weekend following a liver transplant in April last year and Iniesta was delighted to have the Frenchman back playing.
"It was incredible to see Éric Abidal back on the pitch," the midfielder said of his teammate. "It made our hair stand on end, as you say. It was a unique moment.
"He's an example for many people who might be going through difficult moments. To see someone like Abi, who is back playing football after everything he's been through, is incredible. He's a great example for all those people who could need an example like him."