Montgomerie's withdrawal because of sickness followed the decision of former British Open champion - and another former winner of this title - John Daly not to make the trip "for personal reasons".
Montgomerie flew to Canada for a golf day on Monday but, according to his manager Guy Kinnings, fell ill on the journey back to London.
"He was sick overnight Tuesday and all day Wednesday," said Kinnings.
Montgomerie was to have unveiled his third caddie in three weeks, albeit another temporary one.
The eight-time European number one parted company with Alastair McLean following his missed cut in the Austrian Open and hired a local man for the second major of the year.
Kinnings added that a list of some 30 names for a permanent replacement has been drawn up and a decision would be made before next week's French Open.
There had been a doubt about whether Montgomerie would play in Paris, but his withdrawal from Munich makes his presence there more likely.
England's Shaun Webster replaced him at the Eichenried course and was paired with Swede Niclas Fasth - top European in finishing fourth at the US Open - and Indian Jeev Milkha Singh in the first two rounds.