Ryanair chief executive Michael O'Leary confirmed that Manchester United approched them as a possible £25m replacement after the US insurance company AIG as shirt sponsor.
Manchester City fan O'Leary commented that the sponsorship opportunity was "too narrow", he added. "It was too expensive for what it was worth to us."
In July, Ryanair's opened a new base in Manchester with O'Leary wearing his Manchester City shirt despite the fact that it was sponsored by another airline, Etihad.
Last season, Aon replaced AIG as United's shirt sponsor after signing a record €91m four-year deal.