Feyenoord defender Terence Kongolo is wanted by the Black Cats
Kongolo, a member of Louis van Gaal's Netherlands squad for the 2014 World Cup, was previously linked with Manchester City, where his younger brother Rodney currently plays.
The 22-year-old was a regular for Feyenoord this past season, appearing 29 times as the Rotterdam side finished third in the Eredivisie - 19 points off a Champions League place.
Sunderland are set to lose Wes Brown on a free transfer this summer, while another centre-back John O'Shea has only a year to run on his Stadium of Light contract.
It is unlikely that the latter's Black Cats career will be extended much beyond that, having recently turned 35, and the youthful Kongolo, who can also operate at left-back, would surely be viewed as a welcome addition.
Interest from Leverkusen, who fought back to seal their place in next season's Champions League group stages, could throw a spanner in the works however.
Fellow suitors Hamburg finished 10th in 2015-16, a mere five points above the relegation play-offs.