A senior board member of the Birmingham 2022 Commonwealth Games organising committee has resigned because of "growing frustration" at "a lack of transparency".
Jonathan Browning, who was an independent director and previously the chairman of British Cycling, informed the government of his decision on Monday.
He is the second member of the Birmingham 2022 board to quit in controversial circumstances in recent months.
In a letter to Culture Secretary Oliver Dowden - which has been seen by the BBC - Browning explained he was stepping down because of what he considered "the poor functioning" of the board.
He also referred to a "failure to encourage challenge by the directors or to acknowledge the magnitude of risks ahead of the Games in these especially uncertain and volatile times", claiming it was "leading to a culture where over-promising and under-delivering appears to be acceptable".
In a statement, Browning said: "This has not been an easy decision. Unless addressed quickly, [the board] risks major problems as the Games draw closer.
"We can't afford to repeat the experience of the athletes' village, where the pre-Covid shortcomings of the project are still not openly acknowledged."
The resignation of Browning - who was also chair of the Birmingham 2022 contract approvals committee - is the latest setback to the £800m Games, the most expensive sports event to be staged in Britain since the London 2012 Olympics.
Two months ago, escalating costs and construction delays caused by the coronavirus pandemic were blamed for the abandonment of the £500m athletes' village.
There have also been concerns over the building of the £73m aquatics centre at Sandwell, where swimming and diving events will be staged.
"There are many good people involved with Birmingham 2022. The Games still represent a great opportunity for the city, the West Midlands and the UK," Browning wrote in his resignation letter.
"However, this will only be realised if a highly effective board is in place that is prepared to face up to today's realities, the full range of future uncertainties and to make the necessary tough choices."
In July, Commonwealth Games Federation president Dame Louise Martin stepped down so concerns over a lack of diversity could be addressed. The Games organising committee had been criticised for having an almost entirely white executive management team and board.
Browning, Birmingham 2022 and the Department for Digital, Culture, Media and Sport have all been approached for comment.
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