St Johnstone manager Steve Lomas believes Anthony Stokes's winning goal for Celtic should have been ruled out for offside.
Stokes scored the only goal of the game after being set up by Mo Bangura in the 28th minute.
"The referee was fantastic; I thought he let the game flow. But the linesman let him down tonight," Lomas told BBC Sportsound.
"It's not a corner (leading up to the Celtic goal) and it's offside."
Lomas's side knew victory would see them move level on points with fourth-placed Dundee United.
But a Murray Davidson strike was the closest they came to scoring on a frustrating night for the Perth outfit.
"I thought they put in a performance; we were looking for a response after Saturday (5-1 defeat by Motherwell)," said Lomas.
"Unfortunately, yet again we're talking about officials.
"It's come into the box and Bangura has helped it on; (Bangura's) clearly in an offside position. It's so hard when you come here and try to keep your composure as a manager.
"It's killed us. Our boys have put in a magnificent performance: we stuck to our gameplan and Murray Davidson maybe should've done better.
"That being said, I was pleased by the overall performance. You come to Celtic Park and you need a bit of luck and for the decisions to be right. They weren't right.
"I thought a draw would've been a fair result. Obviously, last 10 minutes we're taking chances and leaving ourselves a bit exposed at the back.
"But we were magnificent tonight and we've been let down again."