Chris Rawlinson blamed a lack of confidence after Spalding United’s fourth successive defeat.
The Tulips slipped into the bottom half of the Evo-Stik South table following another 2-1 loss on Saturday.
Jamie Jackson missed a penalty before Gary King put Spalding ahead.
However, Matt Melbourne hit a second-half double for Gresley’s first away win this term.
Tulips boss Rawlinson said: “We are massively lacking in confidence.
“I think the lads are just feeling sorry for themselves, even though one or two said they weren’t.
We just need something – maybe a bit of luck going our way – to get out of this run before it becomes really bad.Chris Rawlinson
“We are severely low in confidence.
“Four defeats in a row, all 2-1, show we are not a bad side but we must be doing something wrong.
“The equaliser came from Ellis Humble’s slip and when the striker nipped in, it was a good finish.
“Gresley’s winner was well worked but I think they only had three chances all game.
“We couldn’t finish our chances – including another penalty – and we had a couple cleared off the line.
“We just need something – maybe a bit of luck going our way – to get out of this run before it becomes really bad.
“We need to take a point and build on that in the next game because otherwise it’s going to be a long winter.
“If players leave, they are not going to be replaced. But we need to stop talking about that situation now.
“We must work hard on the training ground. The players need to start believing they are good enough.
“We’ll have to find a way within this squad.
“Things are going wrong and they are affecting us. It’s important not to be beaten – but we must take our chances when we are on top.
“We should have won the game on Saturday.
“In the previous home game against Carlton Town, we were bang average.
“But we must have created 10 chances, including four one-on-ones, against Gresley.”