Sky Sports sources understand that Sunderland have made a £7million offer for West Ham defender Matthew Upson.
The Black Cats flirted with relegation last season before mounting a late rally that ensured a comfortable mid-table finish.
One problem for Steve Bruce was the way his side struggled to keep clean sheets, making it difficult for the manager to settle on a regular back four.
Bruce is looking to strengthen this summer and is thought to have targeted Upson as a player that could improve his squad.
Sunderland are believed to have tested West Ham's resolve with a bid and will hope their offer is accepted.
Upson has been a key figure at Upton Park since he was snapped up from Birmingham in 2007 but the club endured a difficult campaign last term.
A new regime is now in place with Avram Grant as manager and it remains to be seen how he will reshape the Hammers squad.
Co-owner David Sullivan admitted in May that West Ham may struggle to retain the services of Upson, who was part of England's miserable World Cup campaign.