Despite being born in Argentina, Rojas grandparents were from Paraguay. He hoped of playing for Argentina but the stiff competition made it difficult for him to ever receive a call-up, so he opted to represent Paraguay instead, as he explained in 1999: "My grandparents were Paraguayans and before I played in Argentina, I had already received a call-up to play for Paraguay. Still, I turned it down because my ambition was to play for the Argentina national team, but I sound figured out my chances or slim. Just before the World Cup in France, I was invited again by the Paraguayan Football Association and ended up accepting it and representing Paraguay in the World Cup." He was listed in squad for the 1997 Copa América, and was a participant at the 1998 FIFA World Cup, but did not make any appearances. In total, he received 7 call-ups from 1997 to 1998.