A series of messages indicated that he had been trying to speak to team members over the past 24 hours but none of them had picked up their phones.
Millar was referring to his failure to complete the national championship road race at the weekend after withdrawing from the time-trial championship a few days previously due to a lingering cough.
He then indicated that he had been removed from the Tour line-up.
He has since commented: "The bottom line is that I was selected when they chose the team a week ago and they pulled me because they were worried about my health; that is counter-intuitive because they wanted me to race the nationals to prove I was healthy.”
As that tweet notes, he is not the only British cyclist who will not be competing at the Tour de France, with Sir Bradley Wiggins a notable absence for Team Sky.
Millar is retiring from the sport at the end of this season, but was expected to start his 13th Tour.
In fact, he and a film crew were intending to collect footage there as part of an ongoing documentary project marking his last year of professional competition.
Garmin-Sharp have not yet made any comment.
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