O'Neill didn't think Bulgarian ref Georgi Kabakov was up to scratch as Hoops saw their lead against the Spaniards wiped out in three second half minutes

Martin O'Neill felt Bulgarian ref Georgi Kabakov didn't have "his best game" in Celtic's 2-1 defeat to Celta Vigo.

The Hoops boss felt the whistler missed an "obvious" foul on Callum Osmand as he raced into the box in the first half, and then another on Camilo Duran just seconds before the free-kick that Celta equalised from.

O'Neill was booked for his protests after the latter, but was also left ruing his team's inability to add to the lead given to them by Mika Baur right after the break.

And Javi Rodriguez made them pay with a bullet header and a thunderbolt of a strike to from the edge of the area to turn the game on it's head and give Claudio Giraldez his first Europa League win.

"We conceded a free-kick but I thought that just seconds before that, we had a foul for us," O'Neill told TNT Sports. "The referee has disowned that and given them a foul about ten seconds later. The they score from the free-kick.

"That's just knocked us a little bit but there's still plenty of time to recover at one-each in the game. But that's given them a bit of momentum and they've carried it through.

"If Scales' header goes in to make it 2-0, then we'll get the three points. It's fine margins.

"First of all, I think it's a foul against Osmand in the first half. The referee says VAR were checking it. I don't know what they're checking because for me that's a very obvious foul.

"I thought it was a foul against Camilo as well too just before their equaliser but in the scheme of things, that seldom matters.

"I didn't think it was one of his best games to be perfectly honest but we've been beaten in the game and we've lost three matches now.

"But remarkably, we're still in with a chance. We've got to win and we've got to win here, we've got to win away from home."

Celtic are now on a run of four successive European loses, starting with their unthinkable Champions. League playoff second league collapse away to LASK.

They've now lost their opening three Europa League clashes and no side has ever recovered from such a start to make the knockouts.

But O'Neill remains hopeful his team can find their mojo on the continent and rescue the situation, with five games still to come against Besiktas, Torreense, Omonia, Marseille and Union Saint-Gilloise respectively.

"It has been a little while," he admitted. "We take the lead in the game, if we get the second goal we win the match and it changes the whole dynamic. It didn't happen, that's it - we need to try to find a way to win European games."