work permits

im sure alot of will find this a silly question, but how does the work permit rule work? when does a player become elligible for a work permit, is it after a certain amount of international appearances, of appearances for his club or something, how can i find out without going through a long transfer negotiation to only find out he has to loaned out in the mean time

They have to have played in roughly 70% of their nations internationals over the previous year or two, or they must be of a good enough quality to be seen to be improving the league (though I don't think that's represented in the game).