The Hoops got off to the perfect start when midfielder Ki Sung-yueng scored from the spot in the third minute after striker Gary Hooper had been fouled by Lars Joel Ekstrand, although the official took his time before pointing to the spot.

With four minutes remaining, and Celtic looking as though they had done just about enough to get past a youthful and inexperienced Italian side, Yildirim adjudged Hooper to have fouled Neuton Sergio Piccoli in the box.

Almen Abdi sent Lukasz Zaluska the wrong way with his penalty to leave the stunned home side with one point from two games.

The Celtic boss was in no doubt as to why they his side had not come away with all three points ahead of their trip to Rennes next month.

"It was a disgraceful decision," he said. "Gary Hooper did what he could do to get out of the way.

"Ours was definitely a penalty but the referee deliberated for 20 seconds before giving it. I can't understand that.

"Hooper is very upset and angry as all the players are after putting so much work in to the game.

"To lose two points after a decision like that is hard to take for the players.

"Of course it will (affect our chance of qualifying). It denied us two points when we wanted to enforce our home advantage.

"They can take a lot of confidence from the way they played tonight but at the end of the day if the referee does his job properly we win the game."

Udinese coach Francesco Guidolin, who had controversially left several of his star players out, starting the match with only four regulars, refused to be drawn on Lennon's comments.

"I never talk about refereeing decisions," he said. "That is my style."

He was more willing to admit he was ready to take criticism for travelling to Glasgow with such a young squad.

"I came here ready to take flak," he said.

"I had prepared a bullet-proof vest but I stood by my decisions and I am happy with the draw.

"Udinese have never played with such a young team. It was one of the youngest teams in the Europa League.

"But tonight was worth 100 days on the training field. It was part of the learning curve.

"It was a good performance and the team showed great character.

"I had thought a lot about the decision to play such a young team and the responsibility of being the manager.

"We are a small club operating within our means and there are certain decisions that have to be taken.

"I am happy for the fans who came here, who showed that they cared, I am happy that we got a draw for them."

Celtic defender Charlie Mulgrew emerged from the dressing room crestfallen at losing two points and knowing it could be costly to his side's chances of qualifying out of the group.

"It was devastating," said the former Aberdeen player. "It feels like a defeat after the way we played and the way we held out in the second half.

"To lose a penalty that wasn't a penalty was very disappointing. I seen it again and it wasn't a penalty.

"We were looking at getting the second goal to kill it off and we had the balanced between attacking and defending just right.

"We are disappointed to lose the two points that but we will take confidence from the performance."