Fleet were well beaten 3-0 on home soil on Saturday and now sit seven points adrift of the play-off places.
McMahon’s men have only won once in six National League fixtures and the boss says any talk of the play-offs is “unrealistic”.
He told BBC Radio Kent: “We were a catalogue of errors. Anything that could go wrong or any bad decision you could make was made.
“It was a frustrating afternoon. The better team won without a doubt. They’re a team that for me will definitely be in play-offs.
“We’re too inconsistent, I’ve been saying it for quite a while. We’re too up and down to be a serious contender for the play-offs and promotion out of this League at the minute and we can see today again the work we have to do.
“It’s been an unrealistic thing that people have talked about for us to get into the play-offs. But we’ve got to be better than we were today, forget the play-offs, forget anything else, that was just a rank performance.”
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