The 27-year-old has returned to Elland Road for treatment on the problem ahead of United's home match with Middlesbrough on Saturday.
McCormack had been hoping to add to his tally of 10 Scotland caps in the games against Norway in Molde on Tuesday.
Scotland have already lost Blackburn defender Grant Hanley, Sunderland striker Steven Fletcher and versatile Celtic player Charlie Mulgrew since Friday's 0-0 draw with USA.
"Heading back to Leeds having had to pull out the Scotland squad. Typical," McCormack said through a social network site.
"Just need another 24 hours for this to settle. I'll be fit for Boro 100%. And can't wait for it."