Two clubs and a player can agree everything and still fail to complete a transfer. The remaining obstacle is the state, which decides whether the player may work in the country at all.
Playing football is employment
A footballer joining a foreign club is taking a job, so immigration law applies exactly as it would to any other skilled worker arriving from abroad.
Countries generally require sponsorship by the employer and some demonstration that the role could not reasonably be filled domestically, adapted for sport into objective criteria.
Because the criteria are set by government rather than by the sport, clubs cannot negotiate them, and a transfer fee has no bearing on the outcome.
Criteria usually rest on international appearances
The most common test asks how often a player has appeared for his national team, measured as a share of available matches over a recent period.
National team ranking then adjusts the threshold, so a player from a highly ranked country needs fewer appearances than one from a lower-ranked nation.
The design rewards established internationals and works against exactly the young prospects clubs most want to buy before their value rises.
Exceptions committees handle the near-misses
Systems that use a points or appearance threshold generally allow an appeal, where a panel weighs transfer fee, wages and the league the player is leaving.
Fee and salary function as evidence of quality, on the reasoning that a club paying a large sum has made its own judgment about the player's standard.
That makes wealthy clubs more likely to succeed on appeal for the same player, which is a quiet advantage that never appears in a transfer report.
Loans and satellite clubs route around the rules
A club that cannot register a signing may park him at a partner club in a country with easier requirements, letting him play and accumulate the appearances the permit needs.
This is legal and widespread, and it is one of the reasons multi-club ownership structures have grown so quickly across borders.
Regulators have taken an interest, since the arrangement effectively lets a club acquire players its own jurisdiction would not admit.
American soccer faces its own version
Clubs in the United States operate under both immigration rules and roster regulations limiting how many international players each team may register.
Those roster slots are themselves tradeable in some competitions, which turns immigration capacity into an asset with a market price attached.
The combined effect is that squad building involves counting permits and slots alongside wages, and a signing can fail on either count.


