Copenhagen has reportedly informed Tour de France organisers that it is not realistic to bring forward the start of next year’s race.
Organisers the Amaury Sport Organisation requested the date change to avoid a clash with the Tokyo 2020 Olympic Games, which have been postponed to 2021 due to the coronavirus pandemic.
The Grand Depart of the Tour de France is set to take place in Copenhagen on July 2, with an individual time trial.
Two flat stages are due to follow in Denmark on July 3 and 4, but the rest of the route in France has not yet been announced.
The Grand Tour is scheduled to run until July 25 in 2021, two days after the rearranged Tokyo Olympics are due to open.
There is a direct clash as the men's Olympic road race has been scheduled for July 24, the day after the Opening Ceremony.
The Tour de France is traditionally flexible with its normal July dates in an Olympic year, with many riders wanting to compete at both events with adequate time for rest and travel.
Copenhagen Mayor Frank Jensen, who is part of the Danish Organising Committee, has written to the Amaury Sport Organisation to say the date change would not be possible.
Jensen cited the challenges the date change would pose to the capital city, which is also set to host Euro 2020 matches next June.
"On behalf of partners for the Danish Grand Départ, I have to inform you that it is not a realistic solution to postpone the dates of the Grand Départ by a week,” Jensen wrote, according to Danish newspaper B.T.
"Placing the Grand Départ between the Euro 2020 matches will mean major changes for the Copenhagen route, as it will no longer be possible to pass central parts of the city centre.
"Changing the date will lead to insurmountable legal ties between Copenhagen as a city, the Danish Football Union and UEFA.”
Tour de France organisers reportedly hope to move the start of the race to June 25.
Copenhagen is scheduled to host a last-16 match of Euro 2020 on June 28 at the Parken Stadium.
Jensen also reportedly outlined issues regarding Copenhagen’s hotel capacity, traffic and potential lack of access of fan areas if the race was moved forwards.
A loss of visibility for the Grand Depart due to the clash with the Euro 2020 matches was also cited as a concern.
This year's Tour de France is scheduled to run between between August 29 and September 20, after its original start date of June 27 proved impossible because of COVID-19.