Celtic boss Neil Lennon claimed Old Firm rookie referee Willie Collum let him down on two crucial decisions during the 3-1 defeat by Rangers at Parkhead.
Neil Lennon: "I think he got a couple of big decisions wrong," Lennon said. "He has got a lot of questions to answer and I want to know why McCulloch was still on the pitch, it was blatant obstruction when we were breaking.
"It was a second yellow and they should have been down to 10 men in the second half.
"And I feel let down on the penalty incident for sure. It's a big decision. I have seen a replay of the penalty and it looked soft.
I'm not sure he saw it and I'm not sure why he has given it.
"There was a long way to go in the game and we were trying to regroup but Daniel pulled out of the tackle and Broadfoot went down very easily.
"At 2-1 we were still in the game, at 3-1 it is very difficult for us.
"I'm not going to go on about the referee because I have my own problems with my team but you have to get the big decisions right and that's another big decision that has gone against us - and I will be asking for an explanation."