soxfan121 said:
There's a pretty well established "Cannot Play Against Home Club" rule for loans. Lukaku cannot suit up and play against Chelsea. This influences the loaning club, but only at the outset of the season. It is known that Lukaku can't play against Chelsea (or Barry against Man City) and therefore Everton can choose to buy cover for it (like Naismith) in the transfer window.
Chelsea's deal with Atletico is different. It says that Atletico can play the loan player (Courtois) but must pay $3M to do so. That is not standard and would "influence" who Atletico plays. That is fundamentally different than "he cannot play".
I mean, I get that one is more common and an established practice and that the situations are not identical. I just don't see how the differences should affect the application of the rule, if the rule is what was stated by UEFA. "You can't play Loanee X against us" and "You can only play Loanee X against us if you pay us $5 million" are both attempts to influence team selection. Under UEFA's statement of the rule, that's the only thing that matters. That one is less standard and creates more ex ante uncertainty about the team selection seems completely irrelevant.
Some of the confusion may result from overlapping jurisdictions. Does this UEFA rule apply to purely domestic competition? If not, that would explain why clubs have been enforcing "cannot play against home club" provisions for years in league play. I can't actually recall an instance in Europe where a team tried to prevent a loanee from playing against them, but my memory is not exactly encyclopedic and I haven't tried to research it.