The Chelsea midfielder’s positive test result comes just three weeks aftter similar struck down John Fleck and ruled the Sheffield United midfielder out of the preparatory camp and warm-up games with the Netherlands and Luzembourg.
Fleck also sat out the matchday squad against Czech Republic and now, for the second Hampden game, there will be another enforced absence in the middle of the park following Gilmour’s news.
It’s a wicked blow to the midfielder who played so well at Wembley, and to the manager’s plans after he got the game plan so right in the Auld Enemy clash.
But now it’s up to the others to take Scotland through to the last 16 for the first time and assuming there are no further ramifications from the latest positive case in the camp, there are plenty of other candidates ready to step up against Croatia in a must-win match.
Even then, progress is not guaranteed but is this the team Steve Clarke will stand by to give the Tartan Army the best possible chance of seeing another match (at least) this summer?
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5. RCB - Liam Cooper
Cooper's reliability defensively could edge him a little ahead of Jack Hendry in the pecking order with Scotland required to keep the Croatians at bay first and foremost. Hendry can play from the back but Cooper's experience in what is going to be a high-pressure occasion might just edge it - allowing Scott McTominay to step up and replace Gilmour in midfield.
Photo: ROBERT PERRY
6. RWB - Stephen O'Donnell
To say he went from zero to hero would be a little harsh but should be riding the crest of a wave after an outstanding display against England followed a maligned performance in the opener. Will be tasked with finding means to compliment Ivan Perisic to keep the forward quiet.
Photo: JUSTIN TALLIS
7. CDM - Scott McTominay
Steve Clarke's swiss army knife is sure to feature and will likely be Gilmour's initil positional replacement alongside Callum McGregor and tasked with keeping Luka Modric's influence to a minimum, allowing John McGinn space and time to play. If the formation changes as required he's adept at various roles.
Photo: Justin Tallis - Pool
8. CDM - Callum McGregor
After a brilliant shift against England, same again from McGregor is required to shackle Modric and keep Scotland ticking. Looked back to himself at Wembley and one more busy shift could push Scotland over the line.
Photo: PAUL ELLIS