The striker has endured a frustrating few years on the international stage, but that was set to end after he was called up by new manager Gordon Strachan last week.
McCormack joined up with the squad earlier this week for their game against Estonia in Aberdeen but has returned home with flu symptoms.
The fan-favourite is one of a number of Leeds player to be called up to represent their countries. Paul Green received a late call-up to represent the Republic of Ireland when they host Poland.
Rodolph Austin has jetted off to Mexico to represent Jamaica who are looking to qualify for the 2014 World Cup.
Defender, Tom Lees has once again been called up to the England Under-21 squad. Lees will be looking for another impressive performance when England face Sweden on Tuesday night.
Youngster Chris Dawson will be looking to make his international debut after been called up to the Wales Under-21 squad. Wales are due to play Iceland Under-21's on Wednesday February 6th.