Boro are in talks with West Ham over the 30-year-old England international, who began his career with his home-town club after emerging as one of its Academy's star graduates.
Press Association Sport understands the player would not be averse to a return to the Riverside Stadium if he proves to be surplus to requirement at Upton Park as new manager Slaven Bilic re-shapes his squad.
However, should that be the case, Sunderland, with whom Downing had a loan spell earlier in his career, too have an interest in him and can offer him Barclays Premier League, rather than Sky Bet Championship football.
In addition, if finance is an issue - the Hammers' £5million signing from Liverpool has been paid handsomely during his spell in London - the top-flight club has more muscle at its disposal having managed to stave off the spectre of relegation once again at the end of last season.
But the Teessiders are hopeful that the emotional pull of a return to familiar territory will work in their favour and help them to pull off what would represent something of a coup for head coach Aitor Karanka.
Boro missed out on a return to the Premier League when they were well beaten by Norwich in the Championship play-off final at Wembley, and there is a determination to leave nothing to chance this time around.
Karanka also has an interest in Ipswich's free-scoring Republic of Ireland striker Daryl Murphy with Patrick Bamford having returned to parent club Chelsea and fellow loanee Jelle Vossen seemingly heading for Burnley after the Clarets agreed a fee with Belgian club Genk.
Source : PA
Source: PA