Monk opted for a weakened team and also conceded his tactics had “backfired” after Leeds were beaten by non-league opposition for the second time in their history.
A 1-0 fourth-round loss at Gander Green Lane in the fourth round was a consquence of Leeds’s line-up showing 10 changes.
Monk had taken the same route to the League Cup quarter-finals earlier this season by omitting most of the players who have lifted the club into a Championship play-off spot.
There were debuts yesterday for 20-year-olds Paul McKay and Billy Whitehouse, who were part of a young side deservedly beaten by non-league Sutton, who sit 83 places below Leeds in the English pyramid and are the lowest-ranked team remaining in the FA Cup.
A penalty from home captain Jamie Collins decided matters early in the second half.
The award resulted from a foul by Lewie Coyle on Roarie Deacon and Leeds struggled in response to create any chances as they sought an equaliser on the artificial 3G pitch.
The defeat is United’s first to non-league opponents since their second-round defeat to Histon in 2008, an upset against a team who were also playing at National League level at the time.
Yesterday’s final whistle prompted a pitch invasion at Gander Green Lane as part-time Sutton celebrated a result worth hundreds of thousands of pounds.
Monk said: “It’s a frustrating result. It’s a frustrating performance, but it’s my responsibility. I’m the one who selects the team.
“I made a lot of changes but it didn’t work and it backfired. I take full responsibility.
“When you make that many changes, sometimes it doesn’t help with how cohesive you are.
“Okay, we’ve done that in the cups and reached a quarter-final and we’ve done well in league games when we’ve had to make changes too, but maybe (yesterday) was one step too far or one change too many.
“Everything didn’t go right. That’s what led to the defeat and a poor performance.
“I’m the one who made all those changes so it’s for me to take it on the chin and make sure the players dust themselves down. We didn’t want to see this happen, but it has.
“I don’t like losing any game. It doesn’t matter which game it is. I’m not a good loser and we’re trying to create a winning mentality so when we lose we take it hard.”
Monk’s changes were no doubt made with two away fixtures to follow in the Championship this week, at Blackburn Rovers on Wednesday night and at Huddersfield Town on Sunday.
United’s head coach has guided his side to fourth in the Championship table in his first season in charge, and promotion to the Premier League is a major priority.
Monk said: “We’ve got a game in three days’ time. I have to get the balance right in making sure there’s freshness and energy. We’ve got a lot of games coming up in February.”
With fewer than 48 hours of the January transfer window remaining, Leeds – having sold midfielder Alex Mowatt to Barnsley for a fee in excess of £500,000 on Friday – are yet to make any signings.
Monk, who has targeted West Ham United striker Ashley Fletcher and Norwich City winger Sergi Canos, admitted he was crossing his fingers for recruits before tomorrow’s 11pm deadline.
He said: It’s very clear. I’ve said it all along we need these players, but maybe the club are best to answer when and where that’s going to happen.”
Asked if the loss at Sutton demonstrated the need for more resources, Monk said: “For sure but I’ve said this before (yesterday’s) game. I’ve been saying it for a while now. We need more players and that doesn’t change.”
Fulham reached the fifth round for the first time in six years as they beat Premier League Hull City 4-1 at Craven Cottage.
Evandro cancelled out Sone Aluko’s opener just after half-time, but that proved to be as good as it got for Hull.
Chris Martin put Fulham back in front five minutes later and further goals from Ryan Sessegnon and Stefan Johansen guaranteed their progress.
There was late drama as Fulham goalkeeper Marcus Bettinelli saved two Abel Hernandez penalties in two minutes. Hernandez’s first effort was saved by Bettinelli, but he fouled the Uruguayan as they challenged for the loose ball. Hernandez stepped up to take the second penalty, but again he was denied by Bettinelli.