If you create original art of an unrecognisable footballer, in a completely original team strip, with no logos, and don't mention any clubs or league names you may avoid hearing from lawyers. There is so much different IP you are dealing with here, every one of which has teams of lawyers, both from the original license holder and from those who negotiated exclusive rights:
- The likeness of the footballer (you also would need a model release from the player)
- The design of the kit
- The individual trademarked logos and designs on the kit
- The name of the player, the team, the league
- The ball is probably also recognisable
The fact is, if you come with a great idea for making money from something or someone that's already popular, then all you will get is lawyer's bills. And in choosing football you have chosen one of the most popular areas, and most enthusiastically protected. If you make something, without rights, they MUST sue you, no matter how small you are, to protect their rights (this is how UK law works, people tell me).