McNamara has been widely criticised for how he has dealt with the latest incident in a series of off-field mishaps which have dogged England's World Cup campaign to date.
The coach initially responded to speculation that Hardaker had been involved in a drunken brawl by claiming he was ill and told a BBC interviewer that the media "are just making things up to try and disrupt my squad".
Two days later England announced Hardaker's withdrawal from the squad, citing "personal issues", but on Wednesday Leeds issued a statement revealing their player was in breach of the club's code of conduct for players.
The Rhinos fined Hardaker £2,500, issued a written warning and ordered him to report for pre-season training on November 25.
Speaking for the first time since Leeds blew the lid on Hardaker's indiscretions, McNamara now claims the England management staff were fully involved in the process to sanction the player.
"We have worked closely in conjunction with Leeds," McNamara told a press conference at Hull's KC Stadium, where England play Fiji in their final Group A match on Saturday afternoon.
McNamara insisted the withdrawal of Hardaker, which followed the earlier expulsion of Gareth Hock for breaking an alcohol ban and failing to turn up for a recovery session, has not caused any disruption to his preparations for the Fiji match.
"I said earlier in the week that, as a coach you have to deal with various situations, whatever arise," he said. "That's been dealt with.
"Unfortunately (Hardaker) couldn't reach the standards that were set within the group. In conjunction with Leeds, the matter has been dealt with."
For Saturday's game McNamara has recalled hooker Michael McIlorum, who was thought to be one of the players involved in the original disciplinary breach featuring Hock, but McNamara remained tight- lipped.
"It's a question that is irrelevant to answer at this stage," McNamara said.