The players of Paok went on strike
Gli stipendi non arrivano e così i giocatori del PAOK decidono di scioperare

The players of Paok decided that they wouldn't take anymore of it and so they went on strike for not being paid. They published an announcement that was signed by all 15 players of the roster of Paok and they e-mailed it to the greek media.
It says that it's not their job to secure the future of the club they're playing in but they are professional players and so this strike is a form of warning for the administration of Paok saying in other words that their hands are clean. This absence from today's training and the statement they made is more of a warning that more will follow if they are not paid the next few weeks.