The UCI said Rasmussen was not eligible to race after "documents he was required to provide to Ernst & Young to allow registration were not provided in time".
The governing body did not elaborate.
Rasmussen wrote on his Twitter feed on Tuesday from western France: "Just got taken out of La Sarthe by the evil and powerful UCI. Lifetime ban in effect by the UCI apparently."
Rasmussen's tweet led to some confusion with the UCI and pundits alike mentioning a possible mix-up with fellow Dane Michael Rasmussen, who this year confessed to doping over a 12-year period.
Alex Rasmussen was initially cleared by the Danish Olympic Committee after he missed two tests and failed to provide his whereabouts once in an 18-month period, but the UCI appealed against the decision to the Court of Arbitration for Sport which imposed the ban on him.
There is no lifetime ban on Alex Rasmussen, whose suspension ended on Monday.
"As far as I'm concerned (Alex) is allowed to race for Garmin... I will make some calls," McQuaid had earlier told Reuters by telephone, before writing in an email: "There could be a mix-up with Michael."