The Manual wrote: Foreign limits
There are limitations for how many non domestic players your team can have at any given time. Based on how busy the transfer market is in your country it belongs to a region, deciding how many foreign players you can possess.
Region A
Teams in Region A may have 3 foreign Players and 2 foreign Players with a Work Permit, for a total of 5 foreign Players.
Region B
Teams in Region B may have 3 foreign Players and 4 foreign Players with a Work Permit, for a total of 7 foreign Players.
Region C
Teams in Region C may have 3 foreign Players and 6 foreign Players with a Work Permit, for a total of 9 foreign Players.