Scotland manager Craig Levein could be handed a number of team selection issues after it emerged that four of the squad's players were missing from full training.
Celtic duo Scott Brown and James Forrest were unable to train alongside their teammates today and instead underwent a light session separately.
Cardiff City shot-stopper David Marshall was also absent from the team's 2014 World Cup qualifier preparations along with Hearts defender Andy Webster.
Scotland are due to face Wales tomorrow and Belgium on Tuesday.
