In the lexicon of Old Firm cliches there is one that advises every player to savour the occasion as if it will be his last.

The instruction may seem simple common sense for some of the Rangers players and to the man who will lead them on Sunday, Kenny McDowall. It would be incredible if McDowall's stint as caretaker manager extended into next season and more potential meetings with Celtic. By the time Rangers next take on their old enemy it also could be too late for 36-year-old Lee McCulloch, 35-year-old Kenny Miller, 32-year-old Jon Daly and even 31-year-old Kris Boyd.

No-one takes a moment to stop and smell the flowers on Old Firm day. The hours, and certainly the 90 minutes of actual play - maybe 120 or more if Sunday's one goes to extra-time and penalties - pass in a frenzied blur. But this time the old heads in the Rangers ranks may find it impossible to resist the temptation to pause and take it all in.

It is an idea McDowall will try to use to Rangers' advantage by recalling an inspiring episode of a team-mate in the twilight of his own career. Frank McGarvey was one of his St Mirren team-mates in their memorable 1987 Scottish Cup final victory over Dundee United. Having been on the books at Liverpool and Celtic McGarvey, although still only 31 at the time, suspected his best days were behind him. Instead, the '87 final unfolded as one of the great days of his sporting life.

Something similar could happen for McCulloch, Miller, Daly et al, or at least so McDowall will tell them. "They will probably appreciate it more being at the age they are at," he said. "I can remember playing with Frank McGarvey in '87. Never did he think he would ever win a cup again.

"I will never forget his words. He said to every one of us: 'Enjoy this moment because cup finals don't come every day. You think you always have a chance, but they are few and far between.' He was so right. I am sure that Kenny, Lee McCulloch, Jon Daly, the older guys, will appreciate where they are in their careers and that it could be their last chance to win a bit of silverware in terms of cups."

Cup finals and semi-finals can be romantic, or they can be unforgiving. McCulloch, Miller and the rest may face their last hurrah in Old Firm terms or their age and lack of pace may be exposed by Celtic team which is generally younger and stronger.

"They are a very good side," said McDowall, who sent a decade as a youth and reserve team coach at Parkhead before moving to Rangers in 2007. "We know that to win the tie we're going to have to play well and we're going to have to carry luck. I think you need all these factors. It's the semi-final of a cup. That's a tough game because you are so close to getting to a big game, but you can be so far away. We are under no illusion, Celtic are a good team and we will need to play well to beat them."

So what made him believe Rangers could win? "Cup football is cup football. It's a one-off game and so far we have done well against the Premiership teams in the cup competitions. We're looking forward to Sunday's game. Obviously Celtic are big favourites for this one, it would be a great achievement if we win."

It had been a normal week around Rangers, said McDowall, a remark always liable to provoke sniggers given goings-on at that permanently abnormal club. He meant the training sessions had been routine. "As we get towards the end of the week we will do some tactical stuff but the fitness stuff has just been normal. We have done some TV stuff [background work on Celtic] each day, just snippets, but we are just going about our business and doing our training."

McDowall never played for Rangers or Celtic but in his first five seasons at Ibrox, as first-team coach under Walter Smith and assistant manager under Ally McCoist, he became a seasoned touchline participant in Old Firm dramas. At 51, he has been pushed out into the spotlight on his own for this one. Did he expect to manage any sleep on Saturday night? A smile. "I have no idea how that will be . . ."