Transgender cyclist Emily Bridges will not compete at Saturday's National Omnium Championships after governing body Union Cycliste Internationale (UCI) ruled she is ineligible, British Cycling said.
Bridges had been due to compete in her first women's event in Derby, facing some of the sport's biggest names including five-time Olympic champion Laura Kenny.
British Cycling said Bridges would have been taking part under their "Transgender and Non-Binary Participation policy" before the UCI ruling.
"We have now been informed by the Union Cycliste Internationale (UCI) that under their current guidelines Emily is not eligible to participate in this event," British Cycling said in a statement on Wednesday.
"We have been in close discussions with the UCI regarding Emily's participation this weekend and have also engaged closely with Emily and her family regarding her transition and involvement in elite competitions."
Bridges, who set a national junior men's record over 25 miles in 2018, began hormone therapy last year to reduce her testosterone levels.
"We acknowledge the decision of the UCI with regards to Emily's participation, however we fully recognise her disappointment with today's decision," the British Cycling statement added.
"Transgender and non-binary inclusion is bigger than one race and one athlete - it is a challenge for all elite sports.
"We believe all participants within our sport deserve more clarity and understanding around participation in elite competitions and we will continue to work with the UCI on both Emily's case and the wider situation with regards to this issue."
Reuters has contacted UCI for comment.