Sources in Paraguay say United manager Sir Alex Ferguson wanted to sign Iturbe immediately, but was persuaded to allow the midfielder to join Porto by Jorge Mendes, the Portuguese super agent, with the view to eventually bringing him to Old Trafford when his work permit difficulties were no longer a factor.
But who is Juan Iturbe? Why is Ferguson so desperate to sign him? And how does an Argentine end up playing in Paraguay?
For many in Argentina, Iturbe is 'their' most talented since Lionel Messi - much to the frustration of Paraguayan football, which less than a year ago were building their future around the 18 year-old.
"When I needed them (Paraguay) they were not there," says the 18 year-old. "They did not know what to make of me. So now I've shut the door.
"Going back (to play for Paraguay) would be a backward step. I have decided to play for Argentina. This decision is final."
Born in Buenos Aries to Paraguayan parents, Iturbe has never actually played on Argentine soil. Instead, the attacking midfielder learned his football in Paraguay with Cerro Porteno, where he made a first team debut as a 16 year-old and in the same season was capped at senior level in a friendly against Chile.
But his Argentine roots always left Paraguay wide open to losing their teenage gem and last year the decision was made.
"He's a great champion, who has now been sold at a moderate price," commented former Argentina World Cup star Abel Balbo. "But within a short time he will cost a lot.
"He is the future Messi."
"It makes me crazy when they compare me with Messi," confessed Iturbe. "The truth is that it is a bit difficult, because Messi is number one, the best player in the world.
"At the same time, I'm proud people and the press say that my style of play is similar to his."
While his senior experience came at Cerro Porteno, Iturbe's registration was actually owned by Quilmes, with the Argentines moving quickly to tie the then 16 year-old to a pro deal after he had made his debut to great publicity in both countries.
It was Quilmes which sold Iturbe to Porto during the summer, but not before his family called in Paraguayan legend Jose Luis Chilavert as an advisor.
With rumours of interest from Manchester United and Real Madrid, the Iturbe family were becoming overwhelmed with dazzling offers from agents and investors. His father, Juan Manuel Snr, revealed last season one business group had offered to pay his 16 year-old son €14,000-a-month to represent him until he turned 18.
"Iturbe's parents approached me and asked me to help with this situation," revealed Chilavert. "We sat down and talked about his future and what was in front of him. They're very excited, but the right decisions now need to be made for both him and his family."
"I just think Porto is the right move for me," Iturbe remarked upon the news breaking last season. "I think I can make a nice career there."
Iturbe chose to pen terms with Porto, despite the frenzied speculation in Buenos Aries of offers from United and Rea Madrid.
"Well, in the future you never know what can happen. We'll see ... but for now it is Porto," added the midfielder.
Porto coach Vitor Pereira is already happy with the impact Iturbe has made.
"He is a fast and can unbalance the opposition. He will play on the wings. Or even between the lines, behind a top-class striker. He is a different player to what we have. A player with an enormous capacity for explosion," enthused Pereira.
It's that explosive capability which has Barcelona sports chief Andoni Zubizarreta already scheduling talks with one of Iturbe's glut of representatives, Gustavo Mascardi. But competition will be fierce.