Alex Neil believes Preston North End were denied by an offside goal in their 1-1 draw with Bristol City at Deepdale on Saturday.
Famara Diedhiou converted from close range 20 minutes from time after Marlon Pack had nodded down Josh Brownhill’s corner.
That cancelled out Daniel Johnson’s goal shortly before half-time as the Lilywhites failed to close the gap to the play-off places, that remaining at six points.
"The disappointing thing from our point of view is their goal was offside,” said Neil.
"We've had a look at it back after the game and the lad is half-a-yard offside.
"The linesman who I spoke to said he felt Darnell Fisher may have played him onside.
"But Darnell was the wrong side of the player with it coming from the left-hand side.
"So basically he has guessed.
"For him to have made that decision was disappointing, had they given the correct decision it would have offside and we would have retained the lead.
"When you are in a such a close match and it is a deciding factor, we are obviously frustrated that the right call wasn't made."