The Barcelona forward sat out Friday’s 2-0 defeat of Italy in Manchester with a thigh muscle problem but came through Monday’s training session in Madrid and is expected to line up against the 2010 world champions.
“He trained as normal with the group so he’s okay to play,” Sampaoli told a news conference at Atletico Madrid’s Wanda Metropolitano stadium.
Sampaoli insisted he was not gambling over his captain’s fitness by fielding Messi against Spain.
“If there was the slightest risk, Leo would have said something. The eve of the match against Italy he indicated that he was not in a state to play.
“But here, he did a fitness test yesterday (Sunday), he did another one today and he’s fine… I don’t think there will be a problem tomorrow (Tuesday).”
Former Chile coach Sampaoli last week described the current Argentina team as “more Messi’s side than mine”.
“Football is about the players, what I meant was he has the power to create links and communicate out on the field,” he explained.
“He can generate a lot of stuff… it’s impossible to teach something to Messi.”
“We are in a place where Leo is untouchable,” added Sampaoli, before suggesting his team would be built around the advice he picked up from Messi.
“Leo, you have to listen to him, create situations that will be optimal for him and from there build a team in relation to that.”
However, the two-time World Cup winners will be without Angel di Maria, who hurt his thigh against Italy, and Sergio Aguero, with the Manchester City striker recovering from a knee injury.
Spain boss Julen Lopetegui, unbeaten in the position since replacing Vicente del Bosque after Euro 2016, says whether Messi features or not will have little bearing on his team selection.
Spain haven’t lost a game since Julen Lopetegui took charge after Euro 2016
“When we’re preparing for a game we’re not thinking about what’s in front of us,” Lopetegui said. “We’ve just played the world champions (Germany) and now face the runners-up who have an incredible player, who collectively have improved with the arrival of Sampaoli.
“What I have ahead of me is a valuable game against Argentina, against the World Cup finalists, sure to be one of the best players in history, and this is motivating us to show what we can do and develop a good feeling as a team.”
Spain and Argentina are seen as two leading contenders at the World Cup in Russia which runs from June 14 to July 15.
The last meeting between the countries came in a 2010 friendly in Buenos Aires where Messi scored in a 4-1 Argentina victory.
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