|Full name||Gonzalo Barreto Mastropierro|
|Date of birth||22 January 1992|
|Place of birth||Montevideo, Uruguay|
|Height||1.73 m (5 ft 8 in)|
|* Senior club appearances and goals counted for the domestic league only.
† Appearances (Goals).
Barreto began his career with Danubio F.C., in Montevideo. He started with the youth team and in 2009, at the age of 17 made his debut with the first team. His debut came in an away match against Tacuarembó, in which he came off the bench and won a decisive penalty as Danubio claimed a 2–1 victory.
Barreto's talent attracted interest from big clubs and he quickly made the move to Europe. On 2 September 2009, Barreto went to Rome to sign a five-year deal with Lazio, who bought him for about €1.781 million. However, Barreto was not be able to play for Lazio until he turned 18 in 2010, due to FIFA's restrictions regarding the transfers of minors across different continents.
Barreto established himself as a star of Uruguay's youth teams. He appeared for their under-15 side in 2007
In 2009, Barreto established himself as a key player for the under-17 national team. He competed with the side in the 2009 South American Under-17 Football Championship, held in Chile, scoring twice in their opening match win over hosts Chile. Uruguay progressed to the final group stage where Barreto scored twice more, against Bolivia and Ecuador. With four goals, he finished as the second highest goalscorer in the competition.
Uruguay's good finish meant that they qualified for the 2009 FIFA U-17 World Cup, held in Nigeria. Uruguay were eliminated in the quarter-finals by Spain on penalties. Barreto successfully converted his spot-kick in the shootout. Injuries restricted him to just two appearances at the tournament.
|1.||20 November 2010||Estadio Juan Carlos Durán, Santa Cruz, Bolivia||Chile||1–0||1–2||Copa Aerosur|
- "Bilancio separato e consolidato al 30.06.2010" [2009–10 Annual Report]. SS Lazio (in Italian). 28 October 2010. Retrieved 28 December 2010.
- (Italian) "La Lazio abbraccia Barreto, il nuovo Zarate". CorrieredelloSport.it (Corriere dello Sport). 2 September 2009. Retrieved 5 September 2009.