It's not quite Lionel Messi vs Cristiano Ronaldo, but the debate raging around Andy Robertson and Kieran Tierney is one of the most fierce in British football.
Liverpool's Robertson and Arsenal's Tierney are arguably Scotland's two best players - and, unfortunately for boss Steve Clarke, they are both natural left-backs.
This is rather a unique problem for a manager to have and dictates the way Clarke sets up his team.
In order to field both star men, Scotland have adopted a five-man defence, with Robertson the rampaging left wing-back and Tierney shoehorned in at left centre-back.
This was how Clarke set up his side against Austria on Thursday night, as Scotland battled to a 2-2 draw in their opening World Cup qualifier.
Of course, left centre-back is not a role which is alien to Tierney; during part of Mikel Arteta's tenure as Arsenal boss he favoured a five-man defence with Tierney often impressing as one of the central defenders.
But Arsenal have transitioned to a back four over the course of the season and Tierney looks all the better for the tactical change.
The 23-year-old has established himself as one of the Gunners' most creative players, flummoxing defences thanks to his expert link-up with Pierre-Emerick Aubameyang and Emile Smith Rowed down the left flank.
Robertson, meanwhile, has been one of the best left-backs in the world in recent seasons, helping Liverpool achieve Champions League and Premier League glory.
But, like almost every one of his Anfield teammates, the 27-year-old has struggled to live up to his own lofty standards during a dismal domestic season for the Reds.
Admittedly, Liverpool are still two spots above Arsenal in the league table as they prepare to travel to the Emirates next Saturday. But Robertson and Tierney's contrasting fortunes hint at possible changing of the guard between the pair and add an intriguing narrative to the upcoming top-flight clash.
But what do the statistics tell us? Here, Mirror Football takes a look at the debate which shows no sign of slowing down...
Defensive solidity
As they are left-backs, it makes sense to start by examining Tierney and Robertson's defensive actions before moving on to their attacking threat.
The pair are remarkably evenly-matched in this department but Tierney edges many of the important metrics.
The Arsenal man has made 1.92 tackles and interceptions per 90 minutes this season - for club and country - compared to Robertson's 1.74.
He has also been dribbled past fewer times (0.7 per 90) than the Liverpool star (0.79 per 90) and has made more blocks per 90 minutes.
One area where Robertson has the advantage is in pressuring the opposition, as he presses 7.96 times per 90 compared to Tierney's 7.64 per 90.
Notably, Robertson tends to pressure higher up the pitch than his counterpart, with 2.38 pressures in the attacking third per 90 compared to Tierney's 1.74 per 90.
This is the result of Jurgen Klopp's intense pressing mantra, whereas Arteta is more inclined to soak up pressure with a rigid defensive structure.
On the whole, however, Tierney appears to have been the slightly more solid left-back this season.
Attacking contributions
It's important to look beyond goal and assist numbers to establish who the more potent attacking force is.
While Tierney has two goals to his name this season compared to Robertson's one, the Arsenal man has a lower expected goals (0.5) than his rival (1.3).
Although Robertson has five assists compared to Tierney's three, there is nothing to separate the two Scots when it comes to expected assists. Both players have registered 0.17 xA per 90 this season - meaning they are teeing up shots worth a total of 0.17 expected goals per 90 minutes.
Moving beyond expected goals and assists, the passing metrics show how vital Robertson is to Liverpool's build-up play.
He attempts 86.3 passes per 90 minutes compared to Tierney's 61.5 per 90, and has a higher completion rate of 79.6 per cent compared to the former Celtic star's 75.9 per cent.
Robertson has also averaged 23.5 more touches per 90 than Tierney and has carried the ball an average of 30 yards further up the pitch each game.
That being said, Tierney has a noticeably higher dribbling success rate and has carried the ball into the opposition penalty area 0.74 times per game compared to Robertson's 0.31.
This suggests the Arsenal star looks to work the ball into the 18-yard box and fire crosses from closer range, whereas Robertson tends to deliver balls into the area from deeper positions.
A look ahead
The statistics prove how evenly-matched Robertson and Tierney are, and do not provide a conclusive verdict on which is the finer left-back.
For Scotland, Clarke is likely to continue with his back five but may be wise to consider other set-ups which would add a new dimension to his side.
He could take a leaf out of Austria's book and look at playing Robertson in a holding role in central midfield, just as star man David Alaba - another natural left-back frequently does.
The 27-year-old could partner Scott McTominay, allowing Tierney to play left-back in a conventional back four.
Alternatively, one of the two could play in an advanced role on the left wing, as the stats lay bare how potent they can be going forward.
Time will probably shape the future of the Robertson-Tierney debate, as the former is four years older and may drop back into the left centre-back role, allowing the latter to occupy the more advanced position.
In the meantime, the pair return to action against Israel on Sunday and the Faroe Islands next Wednesday, before they face off against each other in the Premier League.
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