Lionel Messi is in "unbeatable shape" according to Argentina coach Gerardo Martino, who is preparing his side for their Copa America opener against Paraguay on Saturday.

Messi is fresh from helping Barcelona to La Liga, Copa del Rey and UEFA Champions League titles, having led the Catalan club to the treble with victory against Juventus in the European final in Berlin on June 6.

The 27-year-old now switches his attentions to his national side, with Argentina kicking off their Copa campaign in La Serena on Saturday, and Messi has said he believes the group is better prepared than they were before the 2014 World Cup in Brazil.

"I think it depends on the season the players have had," Martino told a news conference on Friday.

"You would have to make an analysis of the previous season. Messi speaks a lot about what happened to him and when we were together at Barcelona, things didn't end well [because we didn't win a title].

"This year, by contrast, he has won everything."

Martino's sole season at Camp Nou saw Barcelona claim the Spanish Supercopa but miss out on the major prizes at the end of the campaign, while Messi struggled with fitness problems in 2013-14.

However, 2014-15 has seen the forward hit new heights with some stunning performances in Barca's run to the treble.

"He comes here fresh from securing those three titles," Martino said.

"He was in superlative form throughout the season. He is in unbeatable shape.

"Last year he arrived at the World Cup without winning any titles and this year he heads into the Copa America having won three and he has been key in those, playing above his usual level."

Asked about Argentina's change in style since he took over from Alejandro Sabella after the World Cup, Martino added: "The footballers play a big part in that and it is their ability to execute those ideas that have helped us. I believe we have consolidated and reinforced those beliefs. And on top of that, we have the best player in the world."

In attack, Sergio Aguero looks set to hold off strong competition from both Carlos Tevez and Gonzalo Higuain for the number nine role, but Martino refused to reveal his preferences.

"The chosen one must be a mix of Aguero, Higuain and Tevez," he joked.

"The one who plays is worth about €50million, just like the other two. But all of the players in the squad are ready to play."

Martino coached Paraguay for five years and led them to the Copa final in 2011, which they lost 3-0 to Uruguay.

"I always said: in my career as a footballer, I owe everything to Newell's," he explained.

"But as a coach, I owe everything to Paraguay."

The 52-year-old also spent spells with Libertad (twice) and Cerro Porteno before taking over the national team.

On his side's prospects in the Copa America, he said: "I judge the team on their performances, but I know that we cannot survive without results.

"I could tell you that this team are in conditions to become champions, but the players already know that. If we can achieve the level of play that we are looking for, we will be closer."