Manchester United are interested in signing Argentina international defender Marcos Rojo amid talk of a 16 million-pound bid for the World Cup finalist.
The 24-year-old reportedly submitted a transfer request at Sporting Lisbon and told them he wants to join United.
And sources told ESPN FC that manager Louis van Gaal is keen to bring in Rojo as he looks to bolster his defence.
United have seen one defensive target, Thomas Vermaelen, sign for Barcelona while another, Mats Hummels, has been given the captaincy of Borussia Dortmund as manager Jurgen Klopp has ruled out letting the Germany international leave.
The summer departures of Rio Ferdinand and Nemanja Vidic mean United, who have switched to a 3-4-1-2 formation under Van Gaal, only have three senior centre-backs in Jonny Evans, Chris Smalling and Phil Jones.
While used as a left-back by Argentina, Rojo could be an alternative to Evans on the left of United's back three, or he could provide competition for the 27 million-pound full-back Luke Shaw.
Manager Van Gaal also has an interest in Ajax's versatile Netherlands international Daley Blind, who can play as a centre-back, a left wing-back or a defensive midfielder, and Real Madrid's Angel Di Maria.
United have made two major signings under Van Gaal, bringing in Athletic Bilbao midfielder Ander Herrera and Southampton left-back Shaw.