McDonald, 34, will be out of action indefinitely, Blues General Manager Doug Armstrong said.
He told NHL.com the 11-year veteran complained of headaches and "wasn't feeling quite right" after sustaining a hit at the end of the second period of Thursday's 3-2 loss in Dallas.
The concussion was the second within six months for McDonald, who sat out 24 games last season after a Dec. 4 concussion sustained during a game at Edmonton.
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