The build-up to Sunday's Old Firm game at Ibrox has been dominated by discussions about match officials since an unknown Celtic source let it be known the club were frustrated with major decisions they believe had gone against them this season - including in the last two matches against Rangers.[LNB]The leak led to a spat with the SFA whose president George Peat, in a scathing statement, questioned the courage of the Parkhead source and the timing of the story.[LNB]While the subtext to much of the fall-out has been about possible bias among match officials, Mowbray, who refused to reveal the injury that could keep Robbie Keane out of Sunday's game, made clear he was questioning incompetence.[LNB]"I would never question the integrity of any referee or question any bias," the Celtic boss said.[LNB]"The game is becoming faster, particularly in Scotland.[LNB]"It is hurly-burly with long balls and they have a very hard job to keep up with play and so I understand the problems they have.[LNB]"It is just a bit frustrating for us all and I'm sure it is for the officials who make the wrong calls.[LNB]"But nobody has ever questioned they make them for any other reason that they have probably not been up with play or not been at the right angle or not been in the right position.[LNB]"I don't look for the rub of the green, just the correct decisions, whichever way they fall." he continued.[LNB]"Whatever level you play, whether it's Champions League finals or Sunday league kids' football, you hope the big decisions are correct.[LNB]"A few weeks ago we discussed this with Hugh Dallas (SFA's head of referee development) and he has said publicly he has been disappointed with some decisions.[LNB]"I was looking for clarification that's all.[LNB]"There have been some high-profile decisions and some not so high-profile decisions which, if you look at them in the cold light of day, are just wrong.[LNB]"I understand Hugh has a difficult job but if something is wrong, what do you do?[LNB]"You can't change the decision but I think it is right that for us to make people who can affect the referees aware."[LNB]The furore has served to intensify the scrutiny that will be on Sunday's referee Dougie McDonald as the visitors seek to reduce the seven-point gap behind Scottish Premier League leaders Rangers.[LNB]Mowbray, though, denied the timing of the leak was perhaps with a view to handing Celtic an advantage and indeed was quick to distance himself from the source of the story.[LNB]"You can look at all the conspiracy theories you want ," he said.[LNB]"The officials have a tough, tough job in any league in the world and I don't think they will carry any burden[LNB]"I'm sitting here quite comfortable.[LNB]"I'm sure you know nothing has come from me because I don't talk to any of you.[LNB]"It's just another story and I'm sure Walter Smith isn't too bothered either.[LNB]"Everyone in football across the world wants the big decisions right.[LNB]"It's 11 versus 11-[LNB]let's go and play the game."[LNB]Andreas Hinkel claims he and the rest of the Celtic team are relaxed about the match officials on Sunday.[LNB]The former Stuttgart defender said: "I don't think there are any concerns about the referees in Scotland.[LNB]"Everyone can make mistakes, we can make them as well.[LNB]"The referees are only human and you can see it in Germany, or in every Champions League game or Europa League.[LNB]"They only give what they see and everybody can make mistakes."[LNB]Celtic could be without Keane who has not trained all week and will be assessed before the lunchtime kick-off in Govan.[LNB]Defender Edson Braafheid did not train today either due to a calf injury and stopper Jos Hooiveld is still out with a hamstring injury.[LNB]Mowbray said: "I am not going to tell you what Robbie's injury is but he hasn't trained all week.[LNB]"I wouldn't want to say how big a blow it is or could be because we hope he will be fit but we will wait and see.[LNB]"I will give the injured players as long as we can.[LNB]"They will have to train tomorrow and have no reaction when they wake up on Sunday morning, so we will wait and see."[LNB][LNB] Barclays Premier League. Click here to bet.