Rangers chief executive Patrick Stewart has spoken to Scottish FA head of referees Willie Collum to seek an explanation over a key decision in the Premier Sports Cup semi-final.

Celtic went through to next month’s final against St Mirren with a 3-1 extra-time win after what was an incident-packed match.

Johnny Kenny had put Celtic in front at Hampden before Rangers were reduced to ten men following Thelo Aasgaard’s challenge on Anthony Ralston.

However, Rangers believed Celtic should also have had a man sent off just before half-time when Auston Trusty’s boot made contact with goalkeeper Jack Butland’s head when the Englishman had both hands on the ball.

Match referee Nick Walsh decided there wasn’t force behind the contact and showed the USA international defender a yellow card but some Rangers players were furious it wasn’t red. VAR officials backed the on-field referee and didn’t ask him to revisit his decision on the monitor.

Rangers chief Stewart has sought an explanation over the decision, which was one of several flashpoints in a match where extra-time goals from Callum McGregor and Callum Osmand settled the contest in Celtic’s favour.

The decision is likely to be explained publicly by Collum in his monthly VAR Review Show, which is...