Out of contract player cannot play in any match. His spot will be empty if you load a saved formation, but the formation saved remember the player slot placement and automatically puts a contracted player in its place. Previously, this was done randomly so the out-of-position chance is very high, but now the system will automatically select the players with the least position penalty first.

You can make a slot empty by placing a player you want to sell onto that position, save it and sell the player. The system will remember that slot and automatically picks a player for you before game start.