Kembali
The Spanish side equalised in the 68th minute as Javi Rodriguez headed home from a cross from a free-kick.
However, seconds before the free-kick was awarded, O'Neill believes Camilo Duran was fouled. Referee Georgi Kabakov had waved play on. O'Neill was booked for his protests after the incident.
Discussing the incident on TNT Sports, O'Neill said: "We conceded a free-kick but I thought that just seconds before that, we had a foul for us.
"The referee has disowned that and given them a foul about ten seconds later. Then 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."
Further pushed on the call, O'Neill then cited the non-award of a foul for a push on Callum Osmand in the first-half. There had been appeals for a penalty from players but they were disregarded by the referee.
According to O'Neill, the referee told him there was a check by VAR on the incident but there was no intervention.
"First of all, I think it's a foul against Osmand in the first half," said O'Neill. 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."