TBH I’m not too sure about what the rules are over in Europe in regards to FIFA players and if they have a union with collective bargaining agreements or not. However in the NFL and NBA they players and teams are bound by that. There are a lot of rules. For example something like the Neymar situation could never happen because players under contract are strictly forbidden to communicate with any other team representative, it’s considered tampering. Magic Johnson just got fined $500,000 for making a joke about a player under contract with the Indiana Pacers on a night time talk show ffs.
Funnelling wages through an outside company is also difficult to do, just because if it were found out, a team would be massively disciplined. In theory it could definitely happen, however the NBA or the NFL would find out eventually, most likely through the media who are trying to break a major major story, and the equivelant of the death penalty would be given to that franchise. Loss of draft picks, management of the club being forced to resign, fines, and the player’s contract being voided. SOmething similar to this actually happened to the Minnesota timberwolves in the early 2000’s.