British rider Liam Phillips's Olympic dream hangs in the balance after he broke his collarbone at the BMX World Championships in Birmingham.
Phillips, 23, was taken to hospital after tumbling over his handlebars, while Shanaze Reade also crashed out but escaped with grazing.
"Crashed pretty hard in Moto 1 and have broken my collarbone," he tweeted.
Broken collarbones can take up to 12 weeks to heal, while the Olympic BMX event starts on 8 August.
Both Phillips and Reade had claimed silver medals in the time-trial in Friday's opening day of elite competition.
On Saturday three-time world champion and London 2012 gold medal hope Reade had serenely advanced to the quarter-finals of the super-cross - the Olympic BMX discipline.
She appeared set to progress after a strong start, only to tumble to the dirt while leading the field at the National Indoor Arena.
Four riders advanced but she failed to qualify despite remounting her bike swiftly and crossing the line ahead of three others who failed to finish after crashing behind her.
"She's scuffed up," White said. "She was going very fast into the first corner, tried to take a nice tight line and just slipped out - the traction just wasn't there."
Abbie Taylor, who squeezed through qualifying to join Reade in the knockout rounds, was also eliminated in the quarter-finals, while Tre Whyte and Grant Hill were knocked out in the qualifying round.
France's Magalie Pottier won the women's world title, with Australia's Sam Willoughby taking the men's event.