Football has been generating a lot of revenue from different sources year on year, and it's got even bigger with the help of sports marketing agencies on the look-out for any means possible to milk a sponsorship deals. The Premier League has been a real money spinner, generating revenue from naming rights, advertising, shirt sponsorship, kits sponsorships, endorsement etc. Recently, even sleeve sponsorships were even introduced.
The biggest clubs across Europe keep negotiating for higher shirt sponsorship deals. Real Madrid are reportedly in negotiations with Fly Emirates for a better deal, commensurate or higher than that of FC Barcelona and possibly Manchester United.