Nah.
'United' and 'City' are (currently, if not historically) THE 'United' and 'City'.
Everybody (bar a supporter of one of the other clubs named United or City) would immediately understand who you were referring to.
I tend to agree. I'd save the moans for situations where commentators refer to "United" when there are two teams on the pitch called United! Day to day, we all know exactly which team we are referring to when calling them "United".