Captain Darren Fletcher is likely to miss Scotland's Euro 2012 qualifiers with Lichtenstein and Spain after coming down with tonsillitis.
The 27-year-old has returned to Manchester United for treatment, although he will be examined by Scotland's medical team at regular intervals.
"Darren Fletcher is suffering from tonsillitis in Manchester but will be assessed by club and Scotland medical staff on daily basis," read a statement on the Scottish Football Association's website.
The SFA have also confirmed that Leeds United midfielder Robert Snodgrass is a major doubt for both games because of an ankle injury.
Craig Levein's squad will travel to their base in Switzerland on Thursday ahead of the weekend meeting with Lichtenstein.
