Middlesbrough chief executive Keith Lamb has already dismissed a bid - thought to be in the region of £6 million - as "derisory", while manager Gareth Southgate has repeatedly insisted the England international is simply not for sale.
However, Downing's decision to submit a transfer request could force their hand, with Southgate admitting when striker Ayegbeni Yakubu made it clear his future lay away from the Riverside Stadium that there was no point in hanging on to players who did not want to be there.
The manager is under no pressure to sell, although he had made no secret of the fact that he will have to raise his own funds if he wants to buy this month.
The club value Downing at closer to the £15m mark but it remains to be seen whether or not Tottenham, who have been admirers for several years, are prepared to go to anywhere near what would be a record transfer fee received by Middlesbrough.
Downing signed a new five-year contract in February last year, but it is understood he has become increasingly unsettled in recent months and is now ready to test himself away from the club where he has become the highest-profile graduate of a productive academy.
The local boy has won 21 senior England caps to date, the last of them in the 2-1 win over Germany in Berlin in November, a game which earned him impressive reviews.
In England Under-21 international Adam Johnson, Southgate at least has a ready made replacement for Downing, although the 21-year-old has had to wait patiently in line and has much less experience at senior level.
Middlesbrough, who beat non-league Barrow 2-1 in the FA Cup third round on Saturday, currently lie in 17th place in the Premier League, ahead of Stoke inside the relegation zone only on goal difference.
Speculation has also linked Tuncay Sanli with Chelsea and Mido with Wigan, although it is Downing's situation which now appears to be reaching a head.