Middlesbrough are back on the trail of Matthew Kilgallon, skysports.com understands.
Gordon Strachan has already brought in six new players this summer, but he is keen to bolster his defensive options.
He has one eye on strengthening at left-back with former Boro man David Murphy understood to be high on his wish-list, but he also wants additional cover in central defence.
A bid for Rochdale's highly-rated Craig Dawson is on the table, but the League One club are refusing to budge on their asking price which has led to Strachan looking elsewhere.
Boro were in the market for Kilgallon in January before he left Sheffield United to join Sunderland on a three-and-a-half-year deal.
The 26-year-old made seven appearances last season but it is believed Steve Bruce is ready to let him leave and Boro are looking to be at the head of the queue with a bid.
However, Boro are not the only Championship club showing an interest with Preston, Leicester and Cardiff also among those keen on the former Leeds man.