Frederik Alves missed Sunderland's Carabao Cup quarter-final at Arsenal due to a 'lack of discipline in training' Lee Johnson has revealed.
The on-loan West Ham defender was notable by his absence from the Sunderland squad that travelled to the Emirates Stadium, with the 22-year-old not even making the nine-man bench allowed in the competition.
And when asked about Alves' whereabouts after the game, Johnson said an 'attitude error' had cost him his place in the squad.
"With Frederik, it was an attitude error that knocked him out of the squad," said Johnson, following his side's 5-1 defeat against the Gunners.
"A lack of discipline in training."
Alves joined Sunderland on a season-long deal in the summer but has had very little gametime during his stay on Wearside and is widely expected to be recalled by the Hammers in January so that he can be sent to another club where he will get games.
The former Denmark U21 international has been left frustrated after making just two league appearances for Sunderland, both from the bench and totalling only 35 minutes.
He has, however, made six starts in the cup competitons, including three in the previous rounds of the Carabao Cup.
Another player absent at the Emirates was first-choice goalkeeper Thorben Hoffmann, but that was simply a selection decision Johnson saying he wanted to stick with Lee Burge as his cup keeper after his penalty shootout heroics- at QPR in the last round had helped the Black Cats reach the last eight.
Academy graduate Anthony Patterson was on the bench as backup, and that meant there was no place for Hoffmann.
"It was a tough one," Johnson said of his decision over who to play in goal against Arsenal.
"I had a three-man decision to make, and I went with Burgey because he got us through [at QPR].
"Burgey and Hoffmann are two number ones really, it's not fair to call one of them a number two, while Patto might go back out on loan, so you have to give the other competing number one a chance and a focus so that they train properly - especially when he was as good as he was in the previous game at QPR.
"I thought he [Burge] did well last night."
Despite the scoreline, Johnson said he was 'proud' of his team's performance against opponents two divisions above them in the football pyramid, but added that there were a lot of lessons that his players can learn when they sit down for their post-match debrief.
He said: "He will show them where they have come up short but we'll also show them where they have implemented the philosophy.
"It's the yin and the yang, and we always try to weight it 85 percent positive and 15 percent things to improve on.
"I think that's the right way to deal with it because what we can't be doing is digging them out for every mistake, particularly every mistake against world-class players when you play at this type of level.
"What we can use it as is as a reference point moving forward for those guys and demand the maximum, really laser-like focus.
Sometimes they don't know what they don't know, but now they know - it's as simple as that.
"We talked about the mind being the athlete and the body being the means, because the mental side of the game and the psychology is so important, but now we have a reference point to really hone in on those standards."
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