If i’m not mistaken, Sávio was on loan to Girona from Troyes FC (Also City Football Group). So, while Girona and City are both in CL, the transfer is really from Troyes to City. Shows the flaws of the system though, and that ownership should be the only thing that matters if there is to be restrictions, regardless if which competitions they participate in.
As for someones suggested solution of transferring via a 3rd team, i think a players registration can only change once pr transfer window (haven’t bothered finding a source for that, but it should be easy enough i guess).
Maybe a loan with obligation to buy could ve the way out. In essence a sale to Lausanne-> loan to United with obligation to buy in january (to avoid same problem next summer/window)