The Argentine centre-back becomes Gus Poyet's second January signing after Marcos Alonso, moving to the Stadium of Light from Estudiantes until the end of the season
The 25-year-old centre-back joins Gus Poyet's Black Cats on a temporary deal until the end of the season and becomes the Uruguayan's second signing of the January window, following in the footsteps of Marcos Alonso.
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"He's a player I know well because we were following him last season in case we went up with Brighton," said Poyet.
"I watched him for about six months when he was with Newell's Old Boys, and the way he plays, understands football and his physical size made me think of him as a potential signing."
Sunderland have hit form in recent weeks, defeating the likes of Fulham and Manchester United (in the Capital One Cup) and have lifted themselves off the foot of the Premier League as they chase survival.
Vergini joins a defence that has improved recently as the club have recorded just one defeat in their last 10 games, conceding only nine goals and keeping three clean sheets in the process.
The Rosario-born defender has earned a solitary cap for Argentina and won the Torneo Final - the second half of the Argentine top flight - with Newells Old Boys under current Barcelona manager Tata Martino.