Mas earned his first call-up to the Argentina national team in August 2015 by Tata Martino as an injury replacement for Pablo Zabaleta. He made his international debut on 4 September 2015, starting in a 7–0 friendly win over Bolivia at BBVA Stadium, Houston. He also appeared as a substitute in the following game, a 2–2 draw with Mexico. A month later, Mas was recalled to the squad during the next window and started both matches as Argentina began 2018 FIFA World Cup qualification with a 2–0 defeat to Ecuador and a goalless draw with Paraguay. He was an unused substitute during the next set of qualifiers in November 2015 before being left out of the squad in March 2016. He was not named to the squad for the 2016 Copa América but was recalled in September, starting in a World Cup qualifying win over Uruguay. He played in a further three matches, all as the starting left back, before being left out for the final four games as Argentina narrowly rescued qualifying in the last automatic spot. Despite Martino defending Mas' repeated selection as a chance to look at players in contention to be taken to the World Cup, he was eventually left out of the squad and has not received a call-up since.