The midfielder can't wait for his club and international team-mate to get back to playing football after the winter break following a lengthy absence
The four-time Ballon d'Or winner is in the latter stages of his recovery from a hamstring injury - which he suffered in the 4-1 win over Real Betis on November 11.
Messi is expected to feature in Barcelona's clash with Elche on January 5 - the club's first game after the international break - and Mascherano cannot wait to line-up alongside his compatriot again.
He told TyC Sports: "I spoke to Leo during all his injury. I know that he's very well, and that he has made a fantastic recovery.
"I'm waiting for him with open arms, both at Barcelona and the national team. He's important to both teams.
"What makes him happy is to be on the pitch, so we hope he can get comfortable again quickly."
In his absence, the Blaugrana have reached the knockout stages of the Champions League but have seen their lead at the top of La Liga eroded, with second-placed Atletico Madrid level with Barca on 46 points.
Messi will find out whether he has been successful in his bid to add to his record haul of Ballon d'Or awards when the winner of the prize is announced on January 13, with the 26-year-old on a three-man shortlist alongside Real Madrid's Cristiano Ronaldo and Bayern Munich star Franck Ribery.