Injuries ruled him completely out of the 1999–2000 season, (aside from an UEFA Cup match against Levski Sofia on 4 November 1999, which ended in a 1–1 home draw, and a Coppa Italia match against Napoli on 16 December 1999, which ended in a 1–0 home win), which saw him transferred to River Plate in Argentina. There, he infamously played only during the club's 2000 pre-season. His only match was a pre-season encounter against archrivals Boca Juniors, and Fonseca helped his club to earn a win by scoring the final penalty in the shootout. A few days later, Fonseca would resign from his contract and join Como in 2001. He retired in 2003 after the coach told him that he was no longer a part of the first team's plans.