There is a limit to how many players you can have in your team, but you can still store up to a maximum of 300 players in your Clubhouse.
Any player kept in the Clubhouse can't be trained or used in matches.
If you want to train a player or use a player in a match, first you need to send that player to your reserves.
You can move Clubhouse players to you reserves as long as you have space in your reserves. Just drag and drop the player from the Clubhouse to your reserves.
*You can't move a player to the reserves if you have no space left.