Flat racing’s Headquarters was all set to play host to 1,000 spectators over each of the three days of the meeting, which begins on Thursday.
However, due to a rising coronavirus rate in large parts of the UK, Prime Minister Boris Johnson has taken steps in an attempt to slow it down.
As a result, plans to introduce spectators gradually back into sporting venues from October 1 have been placed on hold.
A statement on Newmarket’s website read: “Following guidance that the Government’s programme of spectator pilots has been postponed, the Cambridgeshire Meeting will take place at the Rowley Mile 24th to 26th September as a behind closed doors fixture.
“This will be limited to participants, racehorse owners and essential raceday personnel observing the existing strict health and safety protocols that have been in place across British Racing since the sport resumed without spectators on June 1.”
The Government decision to put the return of crowds on hold comes as a huge blow to racing, just 24 hours after a successful pilot event at Warwick on Monday was attended by around 450 spectators.
Earlier this month, Doncaster was all set to allow a restricted crowd to its St Leger meeting – but even before the end of a successful first day, the local Public Health Authority put a stop to the final three days of crowds.
Previously, Goodwood’s hopes of hosting 5,000 at the final day of its big meeting in July were also dashed in similar circumstances.
All cancelled pilot events came at huge costs to the racecourses involved.
Amy Starkey, who runs Newmarket Racecourses as East Regional Director for Jockey Club Racecourses, said: “We respect the Government’s decision to postpone its programme of spectator pilots across sport as part of trying to reduce interaction between people.
“Sadly, this means the Cambridgeshire Meeting will take place without the limited number of spectators who the team worked so hard to prepare to welcome in a safe way. We will now continue to work with the rest of the industry, Government and our local authority on when it might be possible for spectators to return in the future.
“Unfortunately it now looks like we will not have any visitors to a raceday for the duration of our 2020 Flat season at the Home of Horseracing.
“I’m proud of the role Newmarket Racecourses has played in ensuring that racing has been able to continue behind closed doors, as we will be doing again this week.”
Ascot has also confirmed its four scheduled race days in October will take place behind closed doors – including Qipco British Champions Day on October 17.
A statement posted on the track’s website read: “Unfortunately we will not be able to welcome crowds on race days at this time in line with Government policy announced today.
“In the short term, we will be refunding or offering rollovers to all who have booked for our October race days.”
