Hull manager Steve Bruce says he is "shocked" and "angry" after Jake Livermore's positive test for cocaine.
The midfielder has been suspended by the Football Association and his club, who must beat Manchester United on the last day of the season to have any hope of avoiding Premier League relegation.
"We're in a state of shock and disappointment," Bruce told BBC Sport.
"Then you get angry because of his actions. We've never experienced it before so it's difficult."
Bruce added: "If you're going to manage in the big leagues there will be times when it's difficult. You have to deal with off-field problems but it's what I'm paid to do.
"We've had a terrible week, but you dust yourself off and go again."
Bruce admitted it has been "the hardest 24-36 hours I've had in football management", adding: "They're now looking at Jake's B sample - I believe he has to put his actions in writing before Thursday, then the hearing will be whenever it sits."
Players who test positive on match days for illegal "social" drugs - as opposed to performance-enhancing drugs - can face up to a two-year ban under FA rules.
Livermore, 25, has played 39 times for Hull this season after being signed from Tottenham for £8m.
Former England midfielder Jermaine Jenas, who played with Livermore at Tottenham, wants Hull to help the player.
"I've known Jake since he was a young lad and I know deep down he is a good lad," said Jenas on Match of the Day.
"He has gone through some very tough personal issues which have been hard for him. I would like to see Hull help him to some extent because it has been a tough year for the lad."
Former England striker Alan Shearer, also speaking on Match of the Day, said Livermore had let himself and his team down "terribly".
"That is going to live with him for the rest of his life," added Shearer. "He is tarnished with that now for the rest of his life. The timing is disastrous for Hull."
Livermore was not available for Hull's crucial match at his former club