Barcelona needed midfield reinforcements following the departure of Andres Iniesta.
Vidal, who is renowned for his hustle and bustle in midfield, does not appear to fit the typical Barcelona style.
But Messi believes they need his qualities to succeed in the Champions League.
“Barca fans always want players with good feet,” Messi said. “We defend with the ball. Players like Arturo Vidal are necessary.
“He’s the type of player who does everything well, with the ball and also with the muscle that he has.
“Games are getting more complicated and difficult, physique is important and we are always the smallest.”
Arthur Melo was also signed - for an initial €31m - to fill the void left by Iniesta.
He - like Vidal - is yet to start a La Liga match, but Messi believes he could be the club’s heir to legendary midfielder Xavi.
“Those who came are very good,” he said. “Arthur I didn’t know that much about but he seems similar to Xavi.
“He’s very safe and trustworthy. He has the La Masia style.
“Playing short passes, without losing the ball, and he grasped it quickly, the dynamic of the team.”
Meanwhile, Messi has expressed surprise at Real Madrid’s decision to sell Cristiano Ronaldo to Juventus.
“Real Madrid are one of the best teams in the world with a great squad (but) it’s evident that the absence of Cristiano Ronaldo makes them less good and makes Juventus (one of the) clear favourites to win the Champions League,” he said.
“It surprised me. I didn’t imagine him leaving Madrid or joining Juventus.
“There were a lot of teams that wanted him. It surprised me but he went to a very good team.”