Craig Levein, naming his first squad as Scotland boss, told a news conference on Monday: "[Rangers manager] Walter Smith phoned me up and told me about the incident and that he would not be fit to play.
"As he wasn't fit it made it nice and simple for me, so I took him out of the squad and put someone else in."
McGregor has not been called up for Scotland since being banned along with Barry Ferguson after being caught on TV appearing to make V-signs from the substitutes bench before a World Cup qualifier with Iceland at Hampden Park last March.
In a statement Rangers said: "We are aware of an incident involving Allan McGregor in the city centre but we are making no further comment."
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