The defender has played for the Argentina national team, but struggled for consistent form while at the Black Cats.
Boca Juniors are trying to renegotiate the price for the defender after a failed medical.
The Argentine international spent last season out on loan at Getafe.
Sunderland’s Santiago Vergini could leave the club this summer.
The central defender is not a part of the former Rangers manager's first team plans at the Black Cats.
The Black Cats are said to be duty bound to sign the defender after he made more than 20 appearances last season.
The Sunderland coach is reportedly making plans to sign the Celtic defender.
Vergini is currently on loan at Sunderland from Estudiantes.
Santiago Vergini is keen to see Sunderland pick up before the end of the season.
Sunderland defender Santiago Vergini admits he feels more comfortable in the centre of defence.