Scotland World Cup qualifiers: Anthony Ralston & Kieran Tierney out

And Clarke added: “Tony’s been at his club. Tony picked up an injury I think last mid-week in the European game that he managed to play through the Old Firm game.

“Everybody was agreed that [Tierney’s injury] would settle down in a few days. It didn’t settle down so obviously the most sensible thing is for Kieran to go back to his club.

“Obviously, disappointed that Kieran’s not with us. When I named the squad I picked a group of five centre-backs so it gives me options to play different ways.”

Brentford’s Hickey, 23, is fit again after a near-two year absence following major hamstring problems.

When announcing the squad last week, Clarke said of Hickey: “He’s good to go. Whether he’s good to go 90 minutes over two games is a different conversation. We’ll manage him.”

Twice-capped recent Derby County signing Max Johnston is the other right-back option for Clarke, with Sassuolo’s Doig, capped once, boosting options at left-back.

Liverpool left-back and Scotland captain Andy Robertson has flitted between his natural position and left wing-back for the national team in recent years. He is yet to start for his club this season.

Clarke was asked if he was concerned about Robertson’s game time and the head coach replied: “Short answer, no. More elongated answer is he’ll get plenty of minutes on the pitch.

“Liverpool will be challenging for the Premier League, they’ll be challenging for the League Cup, they’ll be challenging for the FA Cup, they’ll go far in the Champions League. So, they’ve got lots of matches to play. Andy will play more than enough football.

“Josh has come in. He came in in the summer and was really impressive. He’s improving, he’s maturing all the time. Obviously, got promotion with his team in Italy this year so a good season in Serie A for him will make him a better player.”

Scotland begin their campaign in Copenhagen on Friday before travelling to Hungary to face Belarus on Monday, with both games to be shown live across the BBC.