Talented left-backs are a bit like auld Corpy buses. You stand for what seems an eternity without one in sight, then all of a sudden three come along.

That is perhaps the feeling that will sweep over Gordon Strachan as he stands at a crucial crossroads with Scotland, wondering just what way our teetering national team will be headed.

In one direction, there is the promised land of Russia and with it, the first major finals for the Tartan Army in what will be 20 years. While a win against Slovenia at Hampden this Sunday won't deliver Scotland to the World Cup - far from it - it will at least keep the avenue open.

The alternative route if a win is not garnered against this European superpower is a road of frustration and misery we have been travelling down for some time now. The song 500 miles is perhaps quite fitting.

There are various selection headaches ahead of that crunch tie this weekend which Strachan will need to get his head around. Most of them will revolve around trying to start a striker who is not playing instead of the unfancied Jordan Rhodes who, well, is.

The one pleasant conundrum the Scotland manager has on his plate revolves around that left-back slot. For years it has been a problem area that saw others from around the park seconded into the role while the likes of Alan Hutton were left to rampage up and down the right-hand side.

Now, it is very much the other way about. While Ikechi Anya is most likely going to line up on one side, it is three-way battle to fill the No.3 jersey on the other flank.

It is a position Andy Robertson has performed so well in since he first burst on to the Scotland scene in 2014 in a friendly against Poland. At that stage it looked to be his shirt for life.

Then came along Kieran Tierney at Celtic and, coupled with the emergence of Rangers in the top flight, Lee Wallace is also back in contention.

Robertson looks set to play against Canada tonight at Easter Road as the six-strong Celtic contingent get rested. However, he is well aware of the challenge he faces to keep both Old Firm full-backs out the team.

The Hull defender said: "Lee and KT are here as well as me. Charlie [Mulgrew] can play left-back as well. Arguably there are four who can play that position.

"We're all having quite a good season and we're all confident. It's for the manger to decide, it's his headache. I'm glad we don't need to pick the team.

“I don’t think if someone plays brilliantly against Canada they are guaranteed to play on the Sunday.

“You have auditions every week when you are playing for Hull or when KT plays for Celtic. Or when any of the boys play for their teams.

“The manager is watching every game and when it comes to calling up the squad he will base that on performances for your club. At the end of the day that’s it.

“The Canada game if you play well it might mean you are in with more of a chance but the manager will make his call in training and what he thinks his best team is for Sunday.

“International football is different. Game to game it changes because you need different things or you see different weaknesses in the other team.

“The manager will make his decision and he’ll think it’s right. There will be two of us disappointed because we have three left-backs but the two will have to deal with that, whoever they are."

With all due respect to the Rangers captain, it is surely the challenge of Tierney that will be causing Robertson the most concern as he counts down his sleeps to Sunday.

The 19-year-old has been a star for Celtic ever since he burst into the team last season under Ronny Deila, and also in Brendan Rodgers' domestically-unbeaten Hoops team this term.

Given how the teenager has adapted to the pressure situations thrust upon him in the Champions League and Europa League, it is no surprise he is already looking like one of Scotland's best players.

“He’s burst on to the scene and he’s done very well," said Robertson.

“From a young age he’s been very consistent and I think all the Celtic boys say Emilio Izaguirre is the most unfortunate guy because he’s done nothing wrong. It’s just Tierney has been so consistent in his performances.

“I think people forget I’m still young as well because Tierney is now the one coming through, but that’s the way it works."

Robertson, however, is up for the fight to keep his place over the coming years, and added: “You say I’m a seasoned pro, I’ve only just turned 23. Not many people say that.

“Luckily I’ve been involved in a Scotland squad from an early age and Tierney has managed to do that now.

“He’s come in at 19 and I’m sure he’ll be in the squad for a long time. It will be a battle for left-back.

“Lee is a wee bit older but he’s not given up on. I went down to the England game and thought he was brilliant, one of the best players on the night.

“He’ll be looking to keep his place.

“At the end of the day we’ve just got to focus on our club football and the internationals will take care of itself.

“All three of us are having a good season so it’s a tough decision for the manager. I suppose it’s a good headache to have."