Don Robertson has opened up on his late call-up to Sunday's Scottish Cup semi-final between Rangers and Celtic.
The whistler was set to be fourth official for the Hampden showdown before Willie Collum pulled up injured in the warm up.
Robertson swiftly took over refereeing duties and he handled the derby fixture well in what was his first taste of the fixture as a whistler.
Reflecting on the game, the 36-year-old, told The Sun: “It was just like a normal game until 1.15pm. I was out pitchside watching the guys warm up and taking in a bit of the atmosphere.
“Willie came off and there was nothing abnormal. When we got in the changing room Willie said he thought he’d done his calf.
“He thought it was serious but he didn’t want to call off. The former SFA doctor John MacLean was working at the game and assessed him between 1.15pm and 1.20pm.
“I thought it didn’t look good and decided I’d better get ready in case he had to call off. At around 1.20pm they made the decision he wasn’t going to start so I had ten minutes’ notice.
“My wife and father-in-law were at the game, and said they were as surprised as everyone when they saw the teams walking out.
“They must have thought Willie had had a hair transplant then realised it wasn’t Willie who was refereeing!
“There were also a couple of looks from the players when we lined up and a couple asked what the story was.
“It’s the only time I’ve refereed without a warm-up. I was careful for the first ten or 15 minutes, I didn’t want to push or sprint too hard in case I got injured.
“People said it was maybe good there was no time to think about the magnitude of things and I was just thrown in. My mentality was it was just a game of football.
“I’ve refereed Celtic and Rangers lots of times previously, the only difference was they were playing each other.
“I was fortunate there were no controversial decisions and the players played in a good spirit. It was so unusual though, in my whole career I’ve never had it happen.”
Robertson added: “As a fourth official 99 per cent of the time your job is off the field, but you need to be ready to step in.
“Willie was a really big support, even though he was devastated to pick up his injury.
“His professionalism was exceptional, knowing his role had changed.
“There was a funny moment when I hadn’t realised he’d swapped with John. I was concentrating so much then 30 minutes in there was a stoppage and when I looked at the technical area John waved back.
“I had to do a double take. I thought they would maybe get someone as Willie’s injury was pretty bad, and if something happened to one of the officials they would have been in real trouble.
“It shows the officials in Scotland work to a very professional standard.
“In a really unusual situation, one nobody expected, as a refereeing team we were able to step up.
“It wasn’t just me taking over from Willie but him standing in as fourth official and John coming in for him.
“It was a real positive for Scottish refereeing.”
