Scotland's preparations for their pivotal World Cup encounter with Brazil have been disrupted by fitness concerns surrounding three key players.Aaron Hickey, Scott McKenna and Lewis Ferguson were all absent from Steve Clarke's group training session on Sunday, with the trio instead undertaking individual work at the squad's North Carolina base.The development comes just days before Wednesday's decisive Group C fixture against the six-time world champions in Miami.Clarke's side currently sit third in their group following a narrow victory over Haiti and a subsequent defeat to Morocco, leaving them needing a positive result against Brazil to secure what would be a historic achievement for Scottish football.Right-back Hickey has not featured since being substituted during the opening 1-0 triumph against Haiti, missing Friday's loss to Morocco in Boston entirely.McKenna, meanwhile, has been dealing with a calf problem throughout the tournament and is yet to make an appearance in the competition.Ferguson's situation differs from his teammates, having completed the full match against the African Cup of Nations holders on Friday evening.There was better news regarding Kieran Tierney, who departed the Morocco fixture during the second period suffering from cramp.The defender participated in Sunday morning's session alongside the remainder of Clarke's squad, suggesting he should be available for the Brazil encounter.Scotland have already secured third place in Group C, meaning a draw against Brazil would virtually guarantee their passage to the knockout rounds for the first time in their history.A victory over the South Americans would confirm progression by securing a top-two finish, while even a narrow defeat could prove sufficient.The Scots have encountered Brazil on four previous occasions at World Cup group stages, managing just one point from those meetings.That solitary draw came in 1974 when the sides played out a goalless stalemate, with subsequent encounters in 1982, 1990 and 1998 all ending in Brazilian victories by scorelines of 4-1, 1-0 and 2-1 respectively.Our Standards: The GB News Editorial Charter