Scotland manager Craig Levein will assess the fitness of Lee McCulloch and Alan Hutton on Tuesday morning before finalising his team to face Spain.
But Hutton is almost certain to miss the Euro 2012 qualifier with a groin injury, with Sunderland right-back Phil Bardsley set to take his place at right-back.
McCulloch served a one-match ban which meant he missed the 1-0 defeat by the Czech Republic on Friday night but a hip problem would have forced him out anyway and the Rangers midfielder remains a doubt.
Levein had intended to name his team on Monday night but McCulloch's absence would force the Scotland manager to make several changes to the line-up he had pencilled in.
Levein had earlier revealed that Gary Caldwell would not start his second successive match after making his first appearance of the season in Prague following double hip surgery.
Scotland were already missing the injured Paul Hartley and Kevin Thomson in central midfield while Barry Robson is suspended. However, Darren Fletcher has brushed off a knock he picked up on Friday.
Steven Whittaker (calf) and Graham Dorrans (hamstring) both trained today after sitting out a session on Sunday with knocks.
With Kirk Broadfoot also injured, Hutton's likely absence would pave the way for 25-year-old Bardsley to make his debut following his surprise first call-up last week.
Levein said there was a "distinct possibility" of a debut for the former Manchester United defender, who was born in England but qualifies for Scotland through his Glaswegian father.
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