Scott McTominay sat out Scotland training on Thursday as Steve Clarke continued his preparations for Sunday's World Cup opener against Haiti.
The 29-year-old Napoli midfielder was conspicuous by his absence at the Atrium Heath Training Centre in Charlotte, North Carolina after going down with a stomach complaint.
Dinamo Zagreb defender Scott McKenna, also 29, was another absentee as he nursed a knock.
However, both men are expected to be fit as the Scots get their Group C campaign under way in Boston during the early hours of Sunday morning.
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Scotland will head into the game looking for a fast start to the competition with Morocco, who made the semifinals in Qatar four years ago, and five-time winners Brazil waiting in the wings.
The match against Haiti will mark Scotland's first game at a World Cup for 28 years.
Meanwhile, Morocco, Scotland's second Group C opponents, have made two last-minute replacements to their squad.
FIFA's official website shows that Marwane Saadane and Amine Sbaï have replaced defender Nayef Aguerd and winger Abde Ezzalzouli on the eve of their opener against Brazil on Saturday.
Real Betis winger Ezzalzouli went off at half-time in the 1-1 World Cup warm-up draw with Norway with a leg injury and was set to undergo scans.
First-choice centre-back Aguerd from Marseille has been out for three months with a groin problem.
Noussair Mazraoui was also forced off with a shoulder knock but head coach Mohamed Ouahbi allayed fears the Manchester United defender could miss out against Brazil.