I don't know why, but when I go to the information page of any player (from any team) I have the button to fire him.
I tested on a bot, to see if it would give some message like "you cannot fire this play" or "this player is not yours", but no... I was able to fire him..
I don't know if someone else also has this super powers, I hope not... Don't know if everyone will be as responsable.. "With great power comes great responsabilities..."
Please try to fix this bug as soon as possible, it's quite dangerous.
I hope I could help.