The home side were awarded a penalty in the 76th minute as Connor Goldson saw the ball ricochet onto his arm from point-blank range.
Despite a poor performance, McManus does believe the Gers were unfortunate to see the home side double their lead from the spot.
“I think even the most avid Celtic supporter would say it wasn’t a penalty kick.
“He knew nothing about it and I couldn’t even believe it went to VAR.
“They got unlucky with that but 2-0 was a fair result.”
If the Ibrox faithful can look past their completely abject performance against the Jupiler League side, then they have every right to be fuming with the official awarding the home side a penalty.
Goldson has got absolutely no chance of getting out of the way of the ball with the Rangers defender less than a meter away from where it bounced up from.
Where the referee expected the Gers man to place his hands remains a complete mystery.
The handball rule has become so harsh on defenders that attackers will just start trying to aim for opposition players’ arms when inside the box.
Rangers won’t stand a chance of overturning the deficit if they put in a similar performance next week.
However, the Gers showed last year their ability to turn ties around at Ibrox last season and if they can rectify the issues they faced in Belgium, they stand a good chance.