Celtic manager Brendan Rodgers said he was "baffled" over the disallowed goal that proved pivotal in his side's 2-0 Europa League defeat by Sporting Braga.
Kelechi Iheanacho celebrated what looked to be a 51st-minute equaliser after charging down an attempted clearance from former Celtic defender Gustaf Lagerbielke, who was put in trouble by a loose pass.
The ball appeared to hit the Celtic striker in the face, but referee Tobias Stieler ruled the goal out for handball and video assistant Christian Dingert stuck with the on-field decision after studying footage for more than two minutes.
There did not appear to be any evidence of an arm being used in television replays, but Braga were awarded a free-kick and the visiting goalkeeper made good saves from Kieran Tierney and Sebastian Tounekti before Gabri Martinez sealed a 2-0 win with five minutes left.
"I can't understand why the referee isn't asked to go and have a look at it," Rodgers said.
"Even if you look at it once, twice, and I'm assuming the guys in the VAR will have watched it more than that, because of the time it took, there's absolutely no way from every angle you look at that he's touched it. It's hit his face, he's gone on and finished it really, really well.
"I think clearly what the assumption is, that it's not conclusive. But I think it's very clear if you watch it -- it's a mistake by the referee.
"That for me is what VAR is about, to correct the wrong decision. So it was a wee bit baffling that he wasn't even asked to come over and look at the screen."
Celtic were trailing to a 35-yard strike from Ricardo Horta, whose shot swerved and dipped but was not particularly powerful or in the corner of the net.
Kasper Schmeichel appeared to misjudge the situation and was slow to move his feet before clawing the ball high into the net.
The Dane had earlier given away possession three times in the opening 20 minutes.
Rodgers said: "It looks like the ball is moving. Of course, he probably will be disappointed with it.
"What's important is, if you make a mistake in the game, which all players can do, you don't follow that up with another two or three. Kasper has made some great saves for us. I think there will be a couple of ones that we'll analyse with him and look to correct."
Rodgers felt his side "started to chase the ball" after the goal and he moved to a back three at half-time.
"I felt we needed to change it at half-time, so we changed the structure of the team, came out on the front foot really well, had opportunities and I don't know why the goal wasn't given. It's a real pivotal point in the game," he said.
"If we get the goal at one each, that breeds the confidence again. I haven't had an explanation as to why it wasn't given.
"But we continued to press and the keeper's made a couple of great saves. We couldn't quite get the goal and of course, at 1-0 when you're chasing, we then conceded a disappointing second goal."