THERE'S only one Leigh Griffiths, as the Tartan Army will no doubt be overheard singing at Hampden this Thursday. Yet so much does Gordon Strachan feel that the Celtic striker has developed personally and professionally in the last four years that the Scotland manager feels that the man who he handed his international debut as the lone striker in a 1-0 win against Croatia in Zagreb in March 2013 must have been his "not-so-good twin brother".

Strachan feels that the 27-year-old from Leith is quite simply a different person circa 2017 and what better way for the Celtic striker to underline his coming of age as an international player of renown than by grabbing a priceless goal as the national team chase the two wins - against Slovakia this Thursday, then Slovenia on Sunday - which would almost certainly see us book a play-off place for World Cup 2018 in Russia. While the Scotland manager said that midfield "fortunately was an area where we are strong", the little man will be more relied upon than ever after his clubmates Scott Brown and Stuart Armstrong withdrew injured.

"From the Croatia game where we won 1-0 [in March 2013] he is a different man altogether," said Strachan, of a man who has had to win over his manager and fend off the best efforts of Moussa Dembele for a starting spot for his club, regardless of the 40 goals he plundered a season previously. "He’s just not the same person. There’s been an incredible change in him.

"That must have been like his not-so-good twin brother that was playing up there in Croatia," the Scotland manager added. "He gave it his best, in terms of what he had physically. But what he knows about the game and how he’s developed since then is beyond belief. Fair play to him because he was a man who two or two-and-a-half years ago was going to go to Hibs on loan again. I keep saying, for all the coaches he’s had and everything else, most of it is down to him."

Griffiths, of course, is coming off his first-ever goal in the Champions League group stages, at the Constant Vanden Stock stadium in Brussels in midweek, merely the latest instalment of the Celtic success story which has given such a shot in the arm to the Scotland national team. The Scotland manager was at Birmingham City v Sheffield Wednesday instead, but was delighted to catch up on almost all of the news, the exception being the muscle injury which appeared to force his talisman Scott Brown off the field early.

"I think we all enjoyed that result," said Strachan. "Away from home anywhere in Europe is hard work and to get a result like that is great."

Much has changed since Scotland went down 3-0 to Slovakia last October. A rather strange match where the final score ill reflected some neat possession play from the Scots, that night in Trnava was Kieran Tierney's first competitive outing for his country. While he has been indispensable ever since, it is still the only time where he has played in his favoured left back role. Strachan stops short of comparing this current Scotland group to the one which performed well in the opening part of the Euro 2016 qualifying campaign, or a team of any other era, but there is a sense in which he can trust this team in their usual 4-2-3-1 shape against anyone apart from the world's very top sides.

"We are getting to the stage now where we think we can play a certain style that will suit us against most. We changed [to three at the back] against England because we think that they are top, top quality. This [Slovakia] is a right good side and they are probably a goal behind England in quality – as you saw – but we don’t have to think too much about the opposing side because of performances."

If the big drama was losing Brown and Armstrong, those of the smaller variety included Leeds United defender Liam Cooper, given the big build-up on Monday, saw himself dismissed against Cardiff City just hours later. "You couldn't have got a bet on that," said Strachan. "We gave him the build-up then bang."

Then there were comments from Ryan Fraser in the local paper, the Bournemouth Echo, saying he was frustrated with his lack of chances at international level, and putting it down to where he plays his club football. "I think we all know it's tongue in cheek," said Strachan. "He's an absolute gem about the place. And Mark McGhee and I are far closer to where he plays than we are to any Celtic player, that's for sure. Ryan doesn't realise he's surrounded by Scottish scouts."

For all that knockabout stuff about 'must win' matches during this campaign, there is no doubt any more. Scotland will need to master all their emotions if they are to record a big Hampden win against one of their qualification rivals, the kind of gut check at the business end of a qualifying group which they have regularly failed, for one reason or another, to achieve in recent times. "There is no doubt about it there will be worrying moments in the game - especially at Hampden," he said. "We have to stay above that panic."

That fabled old Hampden roar will have a role to play. Strachan feels the onus is also on his players to keep the crowd with them. "It’s like going to a musical," he said. "If the musical’s not very good you don’t get up and dance about and sing and tap your feet. I’ve seen a couple of musicals like that and you think ‘phff, that’s rubbish’. So you don’t join in. But you go and see Mamma Mia or something like that, you’ll go ‘oh’ and you’re dancing away because it is good quality stuff. I know it’s not a classic musical but it is good fun.

"We have to give the crowd something," Strachan added. "And it is amazing what turns the crowd on. Is it a shot at goal? Yeah, that does it. Is it a header at goal? There are simple things like somebody chasing back 35 yards to toe-poke it out for a throw-in … that turns the crowd on." Victory on Thursday might not be reliant on Benny and Bjorn's back catalogue, but it would still represent one of Scotland's greatest hits.