5 ways Rangers went wrong as Celtic drubbing shows up transfers, ropey Ryan Kent and keeper conundrum

The post mortem after any Old Firm defeat is usually extensive. When it's a mauling like Rangers suffered at the hands of their rivals and champions Celtic at Parkhead then it's likely to be quite deep.

Giovanni van Bronckhorst admitted he was at a loss to explain how his side could concede goals from areas of specific danger they had highlighted from the Hoops. Namely, the fact Ange Postecoglou's men are quick-thinking and the Light Blues weren't alert to it.

The Dutchman will now try to find answers to that. But issues run deeper than that. To lose in such a manner could almost be accepted if it was a one-off. It has happened to managers over the years - Dick Advocaat when Van Bronckhorst was a player and went down 6-2 at Parkhead. Martin O'Neill who lost 5-1 at Ibrox. But the problem for Van Bronckhorst is that it was a repeat performance of his derby dug-out debut at Parkhead back in February. And failing to learn from mistakes is a bigger issue.

But how did it manage to happen again seven months on? Have Rangers regressed in the last 12 months? How big is the gap to Celtic now apart from the obvious five-point advantage in the table. Champions League qualification can't be ignored as the club prepare to return to European football's top table for the first time in 12 years. However, after a 4-0 defeat in the manner of their derby drubbing fingers will be pointed. Here, Record Sport looks at five possible contributing factors to the rout including areas that might need addressed going forward.

The debate over who would start this season as Rangers No. 1 stretches right back to the Scottish Cup final. When Allan McGregor was introduced for a late Hampden cameo, many felt it was a farewell from the veteran.