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Daryl McMahon conceded defeat in the title race after Ebbsfleet were beaten at Sutton on Saturday.
Fleet are three points behind the U's with only one game left and their inferior goal-difference means that gap is effectively four points. Sutton also have a game in hand.
U's boss Paul Doswell insists his side need to win one of their last two games before they can celebrate promotion. Sutton have been charged with fielding an ineligible player and could face a three-point deduction.
But McMahon said: "They’re three points ahead of us with a game in hand so they need a point out of the last two games.
"In terms of the other stuff, who knows what’s going to happen with that?
"In my mind, it’s done now."
Top scorer Dan Fitchett gave Sutton the lead midway through the first half at Gander Green Lane.
A controversial penalty on the stroke of half-time, converted by Bedsente Gomis, finished Fleet off and sparked wild celebrations from the majority of the 3,142 crowd.
McMahon said: "It was a disappointing performance.
"We started reasonably well for the first 20-25 minutes, played some good stuff but once Sutton scored the first goal, they controlled the game.
"The penalty right on half-time was the killer for us. I’d like to see it again, it did look a little bit soft but to be fair to Sutton, I can’t complain. They deserved to win.
"I don’t think we played well after it went 1-0. I don’t think we moved the ball well enough and I don’t think we moved well as a team after that in terms of sitting too deep.
"In possession of the ball, we didn’t move it quick enough. It was just a disappointing performance.
"With some of the players they’ve got on the counter, Bolarinwa, Stearn, it is difficult."