It's the great Scotland riddle Steve Clarke has not yet had the luxury of confronting.
But on Tuesday the Scotland boss was able to name both Andy Robertson and Kieran Tierney in a squad for the first time - and now he has a couple of weeks to work out how to fit two of the best left-backs in Britain into the same starting line-up.
Clarke said: “The fact Kieran is back available for selection is a great thing because you want as many good players as you can in the squad.
“I’m delighted Kieran is in there, I’m delighted Andy’s in there and we’ll find a way to play.
“They’ve played together before. Gordon Strachan used Kieran as a right-back which was one way to fit them in.
“Kieran can play left centre-back, he can play left of a back three or pushed on as a wing-back.
“He played all those positions for Arsenal towards the end of last season and did very, very well. I think he made a few people in England sit up and take notice of his talent but I don’t think that would be a big surprise to anybody who watched Kieran develop over the years at Celtic.”
