The Cardiff Half Marathon - already postponed from this October to next March - has been put back again.
The next edition of the race will now take place on Sunday, 3 October 2021.
Organisers had hoped to hold two half-marathons next year - the postponed event in March and then another as usual in October.
However, they say rising Covid-19 cases and new lockdown restrictions mean it will not be possible to hold an event like this in March.
The initial decision to move the race from October 2020 to March 2021 had been taken in June.
The next two races will now be in October 2021 and October 2022.
Organiser Run 4 Wales said it had been closely monitoring the ongoing coronavirus situation and the guidance issued by the Welsh and UK governments, whilst making arrangements to try and deliver a Covid-secure event in the spring of 2021 but that this was no longer a viable possibility.
"We had watched with optimism over recent months as lockdown restrictions had eased and successful pilot events across the UK have demonstrated that it is possible to safely deliver mass-participation events," said a statement announcing the latest postponement.
"It is now clear, however, against a backdrop of rising cases, freshly imposed lockdown restrictions and a turbulent winter period ahead that it will not be possible to deliver an event of this size and scale by March of next year.
" Run 4 Wales now plans to deliver a number of smaller events with additional hygiene and social distancing measures in place, as it builds to the return of the Cardiff Half Marathon in October 2021.
"The health and safety of our runners, volunteers, event team and the wider population is of the utmost importance to us.
We have therefore been working closely with the Welsh Government and other mass participation event organisers across Wales and the UK to chart a safe return to events.
" Since its foundation in 2003, the Cardiff Half Marathon has become the UK's third biggest race after the London Marathon and the Great North Run.
It typically sees more than £4m raised for charities and last year 27,500 runners and 100,000 spectators attended the race.
The 2019 Cardiff Half Marathon saw men's winner Leonard Langat from Kenya finish the 13.
1 mile course in a new record time of 59 minutes 29 seconds.
The Newport Wales Marathon has also been postponed twice.
Originally scheduled for October 2020 and pushed back to October, that race will now go ahead on 18 April 2021.