Sky Sports understands that Sunderland are following Portuguese midfielder Paulo Tavares.
The 26-year-old attacking midfielder has enjoyed an impressive campaign for Vitoria Setubal and helped them to a 2-1 win over Sporting Lisbon on Sunday.
Sky Sports has learnt a Sunderland scout was present at the Estadio do Bonfim to see him play the full 90 minutes.
It was the second time in the past two weeks that Sunderland have watched Tavares, who is understood to have impressed.
Tavares had previously spent his whole career with Leixoes before joining Setubal this summer on a free transfer.