Steve Clarke will be forced to make do without the influential midfielder as his side seek their first win at Euro 2020
Billy Gilmour will be unavailable for selection when Scotland take on Croatia at Hampden Park on Tuesday night, but why is he ineligible to feature? Goal is here to bring you everything you need to know.
Scotland are currently preparing for their third and final Group D fixture, which they must win to have any hope of qualifying for the round of 16 after picking up just one point from their games against the Czech Republic and England.
Steve Clarke's side can still qualify as one of the four best third-placed teams if they beat Croatia, but will have to do so without Gilmour, who produced a man-of-the-match performance in the 0-0 stalemate with England at Wembley.
The Scottish Football Association (SFA) announced that Gilmour had tested positive for Covid-19 following the latest round of UEFA PCR testing over the weekend.
The Chelsea star is now self-isolating in accordance with coronavirus protocols, and won't be allowed to return to action until he posts a negative test.
Gilmour will have to observe a 10-day period in quarantine, and cannot have any contact with the rest of the squad during that time, meaning he will also be on the sidelines during the round of 16 if Clarke's men make it through.
However, should his recovery run smoothly, the 20-year-old could be available again in time for the quarter-finals, which are due to kick off on July 2.
Clarke has admitted that losing Gilmour for such an important game is a major setback for his team, but has also highlighted the fact that his absence creates a huge opportunity for another member of his squad to make an impact on the international stage.
"He's upset, as you would expect. He has no symptoms, hopefully, his health will hold up," the Scotland boss said after Gilmour's diagnosis. "Hopefully he'll get back to playing as quickly as possible.
"Obviously a blow for us but a chance for someone else. Billy would have started the game and now he won't, so it's a chance for someone else to come into the team and make themselves a national hero."
England have also been adversely affected by Gilmour's positive test, with Mason Mount and Ben Chilwell now having to follow self-isolation regulations after coming into contact with their Chelsea team-mate after Friday's encounter.
Both players were seen hugging Gilmour after the final whistle, and as a precautionary measure will remain in quarantine until at least June 28, meaning they will sit out the Three Lions' final group-stage outing against the Czech Republic.