The 30-year-old, who spent last season on loan at Everton, has been restricted to second-half substitute appearances in Manchester City's first two games of the campaign, coming on in the Community Shield defeat by Arsenal and Sunday's 2-1 Premier League win over Bournemouth.
His limited role under Enzo Maresca has fuelled speculation over his Etihad future for some time, with City previously indicated to be open to letting him leave either permanently or on loan.
Grealish's situation is only part of a broader push by Sunderland to strengthen their attack before Tuesday's deadline. The club are also pursuing Marseille winger Igor PaixĂŁo, with personal terms for the 26-year-old Brazilian not thought to be a problem, though a club-to-club agreement has yet to be reached.
PaixĂŁo scored 12 goals for the Ligue 1 club last season and would add further firepower to RĂ©gis Le Bris's squad as Sunderland prepare for a first Europa League campaign since their promotion.
The Black Cats have already been active in the market this summer, adding full-backs Thomas Meunier and Dayann MĂ©thalie along with midfielder Jules Ahoka to bolster a squad now facing the extra demands of continental football. Grealish himself joined City from Aston Villa in 2021 for a then-British-record ÂŁ100m, winning three Premier League titles, the Champions League and the FA Cup, but has made just seven Premier League starts across the past two seasons combined as his role at the Etihad diminished under Pep Guardiola and, now, Maresca.
Landing both Grealish and PaixĂŁo in the same week would represent a significant statement of intent as Sunderland look to establish themselves at both ends of the market â competing for proven Premier League and European quality rather than simply topping up numbers.