English Leagues mean that only players from EU designated countries can play without having to qualify for a "work permit", or think work visa. Experience has shown me that work permits are extremely difficult to get, I have had two granted during my 5 years with Maidenhead (one for a left winger when I was low level) and one for a young Brazilian striker, and there are no guarantees that the player will be able to get another permit once his contract expires.
In short:
Any foreign player who seeks a work permit must have appeared in at least 75 percent of his national teams competitive A matches during the previous two years.
The player's national team must also be ranked in the top 70 in the official FIFA world soccer rankings.
The club cannot apply for a work permit on the player's behalf unless it is a member club of the Premier League or the Football League.
When the club's initial application has been approved, the player is granted a valid work permit for a maximum of three years or the length of his contract, whichever is shorter. If the player's contract exceeds three years, the club may file extensions in two-year increments.
There are some very good posts around the place regarding work permits, the laws, and feeder clubs that may help you get around the issue - ie sending the player to Spain or Belgium for three years to qualify.