Neil Aspin admitted his FC Halifax Town side got what they deserved after losing for only the second time this season 2-0 at Forest Green.
First-half goals from James Norwood and Jon Parkin proved enough to see off the Shaymen, who failed to score for the first time this campaign.
Aspin said: “It was a poor performance. I thought we were below-par.
“The first 10 minutes we were OK but we gave away two bad goals and the level of performance wasn’t what I require.
“The second-half, Forest Green had the game in their own hands so they didn’t need to push a lot of men forward and we created few chances.
“All round it’s been a poor display and we have to be a lot better.
“The players have done fantastically well. I’ve been delighted with their efforts last season and this, but if we play like we did today then we can’t sustain being in the top end of the league.
“We’ll certainly start falling down the league - we need to be a lot better.”
The Town boss conceded his team gave themselves too much to do after falling 2-0 down within the first half-an-hour.
He said: “If you go 2-0 down it gives the impetus to the opposition, especially when you’re away from home.
“Last year, the reason we kept losing games away from home was because we conceded too many goals.
“If you’re 2-0 down within 30 minutes you’re going to have a mountain to climb.
“The goals certainly gave Forest Green a lift but I call a spade a spade and we didn’t deserve to win the game.”