United were initially alerted to Aït-Nouri’s availability by his representatives in the final week of the window, according to reports, as they sought a replacement for Luke Shaw who is now 31 years old.
The Red Devils then contacted City and asked whether they could take the 25-year-old left-back on loan for the season but were rejected by their biggest rivals in a deal that looked almost impossible.
Having played just 15 minutes in Enzo Maresca's first five matches in charge, rumours ramped up after the summer window closed, suggesting a January departure may be possible.
Rayan Ait-Nouri has little chance of getting in the City side as he competes with Joško Gvardiol and Nico O'Reilly for a spot under Maresca.
However, according to Football Insider, City have no plans to offload the full-back when the transfer window reopens in January, which means United will have to search elsewhere.
United were also linked with Lewis Hall, who has since signed a new deal at Newcastle, but Antonee Robinson, Alejandro Balde and Myles Lewis-Skelly may be available to manager Michael Carrick as the football calendar heats up.