While a bubble may burst at a certain club devastatingly (oil clubs, should the owners leave), the 'burst' from football would occur gradually. Sky might make a loss from 'dwindling' viewing figures in years t+3, t+4, and when it comes time for Premier League contract renegotiations, the PL might be offered a lesser contract, which would of course then impact the clubs.
Clubs, being hit by reduced revenues, might adjust wage structure. Average weekly salary might reduce by £60k per week to £45k per week. Big money transfers would reduce in frequency, and the transfer market would adjust accordingly.
Sponsorship deals may not be hit as badly. The value of the sponsorships may not change, and if they do, they will have several years to adjust. Like Sky, many are locked in for several years.
This is a contained environment and as such I don't quite see the same risk as you might see in an asset bubble. Structurally, an adjustment may happen, but I imagine it would be gradual.
And I honestly think that football will continue to increase in popularity globally, not the reverse.