Is he friend from the game or facebook ? If he is from fb, you must remove him from friends list.
If this happening, yes it's a bughe can still invite me to play a friendly although he was not in the list of friendship .
if you just ignore it, the only consequence is that during the friendly game you can't do some actions in your teams - like changing tactics, giving sp, training or else.This is so disturbing schedule of my games , because stout player who condition and stamina is reduced before the official games .