The Brazilian had sparked concern among United supporters when he was substituted during the win over Burnley before the international break.
At the time, it appeared Cunha had suffered a hamstring problem, though the club did not officially confirm the injury.
The situation worsened when Cunha withdrew from the Brazil squad for September's international fixtures, prompting questions about whether he would be ready for the blockbuster derby at the Etihad Stadium.
Throughout the break, Cunha has maintained a positive approach and focused on intensive gym work to regain full fitness.
On Sunday, he shared a series of photos from his training session on Instagram, accompanied by the caption: "Sunday's," with a smirking smile emoji. While the post's meaning is open to interpretation, the message has sparked optimism that he could be ready to return to action against City.
United manager Ruben Amorim will be encouraged by any news on Cunha, who has been central to the team's attack this season. Alongside Cunha, Amorim is awaiting updates on the fitness of Mason Mount, Diogo Dalot and Lisandro Martinez.
Mount was substituted at half-time against Burnley, Dalot withdrew from the Portugal squad with a muscular problem, and Martinez has only recently returned to training following a long-term injury absence.
A fit Cunha could significantly bolster United's attacking options for the derby. In recent seasons, United have often entered the fixture as underdogs, but their strong early-season form suggests they could challenge City more assertively this time.
Amorim will hope to field his strongest side as the two clubs prepare for one of the most eagerly anticipated matches of the campaign.
Chelsea’s teenage forward Estevao has admitted he is surprised at how quickly he has become a key part of Enzo Maresca’s plans, describing his early weeks at Stamford Bridge as "the happiest moment of my life."
Manchester City's Jeremy Doku reserved special praise for Kazakhstan youngster Dastan Satpaev after their sides met in Astana, despite Belgium running out 6-0 winners.
The Premier League and Manchester City have reached a settlement, drawing a line under their protracted battle over sponsorship regulations.
Nottingham Forest have parted ways with Nuno Espirito Santo, with the Portuguese coach sacked early on Tuesday after tensions with owner Evangelos Marinakis reached breaking point.
