The news was confirmed by the Scottish FA today, meaning the 20-year-old will have to self-isolate for 10 days and will miss the Croatia clash at Hampden Park tomorrow night.
"The Scottish FA can confirm that a member of the Scotland national team playing squad, Billy Gilmour has tested positive for Covid-19," the SFA said.
"Having liaised with Public Health England since the positive test was recorded, Billy will now self-isolate for 10 days and therefore miss tomorrow's Uefa EURO 2020 Group D match against Croatia at Hampden."
Following Friday’s draw with England at Wembley, in which Gilmour made his first start for his country, Scotland must beat Croatia to stand a chance of progressing from Group D into the Euros’ knockout stage.