Amazon cameras are currently following City boss Pep Guardiola and his team throughout the 2017/18 season for a behind-the-scenes look at the moneyed club in a deal said to be worth £10m. It is expected to launch on the e-commerce giant's video service in the autumn.
But the series will take a big hit if the cameras are unable to film at one of the single biggest games on City's calendar.
Rather than a petty act, BBC Sport explains that United are simply unable to accommodate even more camera crews and broadcasters than they have already granted tunnel access to, meaning there was little option but to deny the request from City and Amazon.
The report notes that as many as 23 different television rights holders have made requests for the game, leaving no room for City's cameras. It is said that United decision makers feel the tunnel area will already be too crowded and have given priority to Premier League broadcast partners.
Amazon is not a partner in the league's £10bn broadcast agreement.
It means the production crew working on the City documentary will have to think of a new way to include the Manchester derby in the series without the availability of behind-the-scenes footage.
When it eventually does appear on the Amazon Prime platform next year, it is expected to be similar to existing series following NFL franchises Los Angeles Rams and Arizona Cardinals.