كتب : وكالات
The 22-year-old defender moved on a season-long loan with an option of a €4.5million switch next summer.
Guillermo has one cap for Argentina in which he scored a debut goal against Costa Rica in January.
On the other hand, Nicolas, who is also on loan at Roma, is a regular for the Albiceleste as he took part in every game of the 2010 World Cup.