A raft of academy players were included on Lee Johnson' s bench for the 5-1 defeat to Arsenal at the Emirates Stadium, and Lee Johnson confirmed afterwards that the West Ham United loanees' exclusion was neither injury nor COVID-19 related.
It's understood the decision was related to a minor disciplinary breach on the training pitch in the build up to the game.
The Dane has struggled to force his way into the side on a regular basis since his arrival in the summer, and West Ham United have the option to recall him next month.
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Johnson has previously admitted that he does not expect either the player or the parent club to be satisfied with his game time.
Sunderland's head coach also confirmed that Thorben Hoffmann's absence from the squad was neither injury nor COVID-19 related.
Johnson was eager to reward Lee Burge's excellent form in previous rounds of the competition, and to give Anthony Patterson a valuable matchday experience.
Patterson looks increasingly likely to return to Notts County on loan, having made a major impact in his initial spell there.
As it stands, Hoffmann is available to return against Doncaster Rovers on December 27th.
"It was a tough one," Johnson said.
"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 did well tonight."
Johnson said he was proud of his players for their performance at the Emirates, and said it would serve as a valuable lesson as attention switches back to the League One campaign.
"We will show them where they have come up short but we'll also show them where they have implemented the philosophy," he said.
"It's the yin-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.
"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."
Sunderland’s defeat means their cup campaigns are now concluded, with no distractions as they chase promotion from League One over the final 24 games.