If the player has left your club completely, you will need to detach them from your club..
Note: You will only be able to remove players from your club if they are not league registered. If they are league registered you will need to contact your league and ask for them to be de-registered so they can be detached.
1. Go to Clubs Portal > Ensure you're selected as the correct club > Navigate to the 'all players' tab.
2. Check the checkbox of the player you wish to detach (or multiple checkboxes) and click "detach".
3. 'Detach player' to remove them from your squad list. You can always add them back if necessary.