The 32-year-old only left England for Toronto FC 11 months ago, but he is understood to have had a medical on Wednesday with the Black Cats.
If Defoe completes the move in time he could even face his former employers Tottenham at the weekend, with Gus Poyet's Sunderland side travelling to White Hart Lane on Saturday.
"I felt so sharp (during his run through on Wednesday)
All that hard work has paid off
I can't wait to start scoring goals for Sunderland," Defoe told the Mirror.
"Everybody knows how much I love English football and I still feel that I have a lot to offer.
"People might look at my age, but I have always looked after myself and I hope I can show that with my performances."
Speculation has increased over Defoe's future in the last week after he revealed on Twitter that he was back in Britain on January 6.
The former Portsmouth forward tweeted: "Just touched down in the UK from south of France,was training with my fitness guy feeling stronger than ever! #Ready."
In the last 48 hours the noises linking Defoe with Sunderland have grown increasingly encouraging, but the deal could still be dependent on Jozy Altidore.
The 25-year-old United States international had been touted to replace Defoe at Toronto in a straight swap deal, although that move would have to be approved by the MLS, which operates an allocation policy.
However, it is a deal which could suit all parties with Defoe returning to the Premier League and Altidore having struggled to live up to the £6.5million fee and reputation with which he arrived from Dutch club AZ Alkmaar during the summer of 2013.
Poyet has made no secret of his desire to add firepower to his squad - which has managed just 18 goals in 21 Barclays Premier League games so far this season - during the January transfer window, and Defoe certainly brings that.
He has been prolific through his club career and has scored 19 times in 55 senior appearances for England.
By contrast, Altidore has found the going tough on his return to England's top flight, where he spent a season on loan at Hull earlier in his career.
His 52 appearances to date have yielded just three goals, and only one of those has come in the league, in a 4-3 home defeat to Chelsea in December 2013.
Altidore has found the back of the net only twice this season to date, for his club against MK Dons in the Capital One Cup in September last year, and for his country in a 2-2 draw with Colombia almost two months later.
Should the double transfer go through, Sunderland would have to complete all the paperwork by lunchtime on Friday in order for Defoe to make his debut against Spurs.
Source : PA
Source: PA