There are only a few scenarios where a player would effectively be sacked. Either the player has committed a crime that is likely to deprive him of his liberty (ie. jail sentence), OR he has done something that would prevent him playing football.
So a car accident sounds a possible candidate, if he was maybe drunk, under the influence of drugs, hit someone, left the scene. Or even all of those things. But surely we'd have heard about it before now?
The second one is failing a drug test. If he gets a ban from football, that means he can't fulfil his contract, so he's effectively sacked himself. That sounds more likely to me.
Just to reiterate - I don't know anything, I'm just guessing, like everyone else.