Primera division teams are allowed 5 non-Mexican players, correct? (I assume that is on some sort of senior team roster.) Does this refer to players without Mexican citizenship? Does Mexico have a permanent residency status, and if so, does a player as that status still count as an international?
Concacaf.com ran a story on Santos picking up Spanish midfielder Marc Crosas, adding that the move was made possible by Daniel Ludueña obtaining his Mexican citizenship. The english Wikipedia page for Santos Laguna has been updated to list Ludueña's FIFA eligibility as Mexican.
That seems to imply the roster rule is pretty strict--permanent residency or other visa statuses aren't enough, you need actual citizenship. Is it common for players to apply for and be granted citizenship?