Hull City boss Steve Bruce believes he "let down" midfielder Jake Livermore, who has avoided a Football Association ban for testing positive for cocaine.
Livermore, 25, failed a drugs test after his newborn son Jake Junior died.
The FA ruled he should not be banned because of "the specific and unique nature of the circumstances".
"I should have realised that he was in trouble and in a dark place, but you carry on and just think he's lost a bit of form," said Bruce, 54.
"I said to my staff on numerous occasions last season that there was something not quite right with Jake, but I didn't identify what it was. I feel like I let him down a little bit."
Bruce told BBC Radio Humberside the club would do "everything we can" to ensure the player gets the help he needs.
Livermore has not played for the club since the 1-0 defeat by Burnley on 9 May, two weeks before the club were relegated back to the Championship.
Former Manchester United defender Bruce does not expect him to return to first-team action for at least three weeks.
The Tigers boss said he was "shocked and angry" at the time of the positive test, but acknowledged he had not known the player's personal circumstances.
"In this macho industry of alpha males, people don't want to ask for help," he said. "Sometimes it takes a bigger man to ask for help and I think Jake has realised that.
"We all think we're Arnold Schwarzenegger or Tarzan and it's not the case."
Bruce said Livermore understands "some people will never forgive him".
He added: "He's made a mistake, he's apologised and he wants to get back to a part of his life which he wants to do - playing professional football."
The former Tottenham player returned to training on Thursday after serving a club and FA suspension pending the outcome of his disciplinary hearing.
Bruce has backed him to have a big impact on Hull's promotion chances.
"He has got a huge part to play between now and the end of the season. His challenge now is to make us better and get us back to the Premier League," he said.
"I'm sure he's determined to get back playing and get back to a level that got him on the edge of England selection. That's what he needs to aspire to again."
Hull, who are second in the Championship after five matches, visit leaders Brighton on Saturday.