Sunderland have clinched a �2.5m deal to sign Derby County's Estonia goalkeeper Mart Poom.

Poom has been on loan at The Stadium of Light since November - although injury has so far prevented him from playing.

The final price tag for Poom is understood to be dependent on Sunderland remaining in the Premiership and Poom playing a certain amount of games.

Sunderland manager Howard Wilkinson believes the 30-year-old will be a valuable addition to his squad.

He said: "It's great to be able to secure the services of a much-sought after keeper.

"Poom has attracted interest from some of Europe's top clubs. He's an experienced and proven Premiership goalkeeper.

"I've watched him closely for some years now and have been very impressed."