Clubs need a license in order to enter UEFA/FIFA approved competitions. If the ESL can be considered a tournament of friendlies and it doesn't interfere with your official matches, it shouldn't be a problem. Finding room for said tournament within the FIFA calender without pulling out of one or more cup competitions seems pretty much impossible and that's where UEFA might be able to revoke licenses and effectively ban clubs.
LEGAL CRITERIA
Article 43 - Declaration in respect of participation in UEFA club competitions
1 The licence applicant must submit a legally valid declaration confirming the following:
a) It recognises as legally binding the statutes, regulations, directives and decisions of FIFA, UEFA, the UEFA member association and, if any, the national league as well as the jurisdiction of the Court of Arbitration for Sport (CAS) in Lausanne as provided in the relevant articles of the UEFA Statutes;
b) At national level it will play in competitions recognised and endorsed by the UEFA member association (e.g. national championship, national cup);
c) At international level it will participate in competitions recognised by UEFA or FIFA (to avoid any doubt, this provision does not relate to friendly matches);
d) It will promptly inform the licensor about any significant change, event or condition of major economic importance;
e) It will abide by and observe the club licensing regulations of the licensor;
f) It will abide by and observe the UEFA Club Licensing and Financial Fair Play Regulations;
g) Its reporting perimeter is defined in accordance with Article 46bis;
h) It will be accountable for any consequences of an entity included in the reporting perimeter not abiding by and observing items e) and f) above;
i) All submitted documents are complete and correct;
j) It authorises the competent national club licensing administration and national club licensing bodies, the UEFA administration and the UEFA Organs for the Administration of Justice to examine any relevant document and seek information from any relevant public authority or private body in accordance with national law;
k) It acknowledges that UEFA reserves the right to execute compliance audits at national level in accordance with Article 71.
That's fair .. but
- Making a rule does not make it legally binding
- Specifically B & C could be interpreted as UEFA telling clubs who/how they can do business (very sketchy area)
In normal circumstances, it might be able to fly or at least not be seen as blatant protectionism that would require court action, but ..
- My view is the very nature of UEFA's response (extremely retaliatory, punishment for something never actually done, clearly sending a message to others) shows they intend to use in the worse way you can interpret it.
We will see, my bet is UEFA will regret this one ..