Messi's form and demeanour were the subject of much debate during the 2013-14 season, with former Blaugrana assistant coach Angel Cappa going as far as to suggest that the No.10 had lost his passion for football.
Ardiles does not agree - but he does believe that Messi feels more comfortable with Argentina, something he attributes to national team boss Alejandro Sabella building his attack around the 26-year-old.
Consequently, the 61-year-old believes the Albiceleste can head into this summer's World Cup with real confidence.
"We have a very good team and we have the best player in the world in Lionel Messi on our side, so there is every reason to be optimistic," Ardiles wrote in the Times of India.
"All eyes, of course, will be on captain Messi. Before the last World Cup [in 2010] he was incredible for Barcelona but not so good for Argentina.
"This time, it's the other way around: he hasn't had the best season with Barcelona, but for Argentina he has done extremely well in the qualifiers, where he scored more goals than anyone else.
"For us to win the World Cup, he has to be at his very best and I think he could be.
"This is because Alejandro Sabella has played a big part in giving him confidence and letting him play in the position he wants to play.
"Now he looks much happier playing for Argentina."