REVEALED: The celtic injury that has shone a light on scotlands youth development problem | Rare Historical Photos

The current understudy is Colby Donovan. And when the 19-year-old appeared on the team sheet for the first leg of the Champions League play-off against LASK, 60,000 fans looked to the heavens and said a silent Hail Mary.

Their prayers were answered when he stepped up to the plate and turned in his most mature performance so far. You wouldn’t have known that from the reaction when Martin O’Neill coughed to the news that Johnston needs a scan to get to the bottom of his latest ailment.

The online clamour for an experienced replacement was such that you almost wondered if Donovan’s display against the Austrian champions had been a trick of the light.

Time might show that the teenager has more in common with Anthony Ralston than he does with Danny McGrain. No one knows that for sure yet, and that’s pretty much the point. Unless he gets a run in the team, they never will.

Hearts are another club with a decision to make over a young prospect. James Wilson appeared as a second-half substitute against Rapid Vienna, replacing erratic Jamestown Analytics signing Pierre Landry Kabore.

A lack of minutes almost forced the Scotland Under-21 player out of Tynecastle last season. He joined Tottenham Hotspur on loan before returning to Edinburgh, coming off the bench to score a 25-yard screamer the other night.

A 12-team Premiership does little to encourage player production. Some managers might tell you they have neither the time, the patience nor the job security to nurture and develop teenagers.

Regardless of whether it’s a football club or a two-bit cafe bar in Gourock, the same principle applies. Young adults need time and confidence to find their feet and iron out the rough edges. Treating them like a disposable water bottle – there to be emptied out then cast to one side – is shoddy and self-defeating.

Sometimes the only way to find out if young players have what it takes to stay afloat is to throw them in at the deep end and see if they can swim. When a kid does get his water wings, it’s usually because the club has absolutely no alternative.

Kieran Tierney claimed his first team chance at Celtic when Emilio Izaguirre was suspended after a red card against Ajax. After a strong performance against Fenerbahce in the Europa League, the full-back never looked back and made the club a packet when he left for Arsenal.

But for injury, Johnston might also have left for the English Premier League this summer. A move to Everton is off the cards – for now – and the Canadian’s stroke of bad luck really should create an opening for Donovan. Only a fool would stake the mortgage on his chances.

It makes no sense for Celtic, Hearts, Rangers or any other club to spend seven figures a year on player development and see little or no return. If they can’t compete with the transfer fees paid by clubs in the top five leagues – and everyone accepts that they can’t – then they need to find another way.

When they spend more than they should on overseas imports, it’s a consequence of their own inability to produce a steady stream of homegrown, oven-ready talent.

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Scotland’s senior clubs gather in St Andrews on September 4 to ponder why other countries do youth development so much better than they do.

Some prefer to blame the exodus of young players to England post-Brexit and send those left behind to play in the Lowland League rather than own up to the fact that they are getting it wrong.

It’s quicker and easier to import a job-lot of journeymen and jobbers to Scotland, aided by a governing body exemption system which hands out work permits like parking tickets, than it is to actually fix things.

The Scottish FA wants to get clubs round a table to get to grips with the issue. And those who don’t respond to a big stick might find a carrot easier to digest. Incentivising teams to give young players an opportunity should be a no-brainer.

Fail to do anything at all, and Scotland manager Sebastien Pocognoli will feed off slim pickings while the performances of clubs in Europe are unlikely to get better. The likes of Wilson and Donovan will be the exception, and not the rule.

In the here and now, Celtic’s second leg in Austria will provide a sterner test of Donovan’s first-team credentials than the 3-0 win in Glasgow when the Scottish champions rode their luck before earning a real chance of a £40 million windfall.

The opening stages of the game felt like a flashback to the days when Nir Bitton would plug the backline in godforsaken places like Be’er Sheva and Astana after they left it too late to sign new players.

Even now, the need for a physical, box-to-box midfielder to come in, replace Arne Engels, boss the midfield and offer some protection to the back line is as glaring as it was when they won their last Champions League qualifying play-off in 2017.

Watching Cameron Carter-Vickers and Auston Trusty exposed in their last two games against Dundee United and LASK, the thought occurred that the return leg could still be one of those torrid, seat-of-the-pants affairs.

Come through a test of nerve and a move for Torino’s Gvidas Ginetis should be firmed up, while Chelsea left-back Landon Emenalo still looks more likely than not to pitch up at Parkhead.

A goalkeeper is still on O’Neill’s list of targets and, beyond that, the biggest question mark surrounds their plans for right-back if the scan results deliver bad news on Johnston.

Either they sign a high-quality loanee from England or overseas and develop a player from another club.

Or they show a genuine desire to make the academy pay its way by giving one of their own a proper chance to show that he can mix it with the big boys.