Being sent off is a punishment for the player AND the team, meaning you indeed cannot sub him. Furthermore 2 yellow cards will ban the player for the next game while an immediate red card will ban him for the next 2 games.

NB: a red card received in eg. a league game will punish the player for the next league game. He'll be able to play in CL and Cup.

PS: don't worry too much about possession. It doesn't mean a lot in Top 11