You squash the grape & it sticks to your foot. ;-)
To me, players are well within their rights to sue but it will suck that any legal fees & damages will come from the club's coffers, not the f**kwit(s) pockets who approved & administered what non-approved substance may have been taken.
ASADA will go after the players, and they don't need to prove any sort of knowledge/intent.
The players will sue the clubs for loss of earnings. They might not have known, but even if they did proving intent on the balance of probabilities will be tricky. The clubs might even settle out of court to get it out of the public eye ASAP.
The clubs will then only sue their employees for some form of negligence or breach of contract IF THEY CAN. There is often vicarious liability protecting the employee from being personally liable. And because the players' contracts were with the club and not the individuals, it's the club as an entity that owes them a duty of care.
It's a nice big clusterf**k.
Even if this wasn't the case, players would be suing the club because the club has the money (well, more than the individuals do anyway). You don't sue people without money. Eventually, the assistant trainer's salary is going to run out and players are out of pocket.