A Paralympic champion cyclist has suffered multiple injuries after being involved in a hit-and-run crash with a van while cycling near Bridgend.
Simon Richardson, 44, was thrown from his bicycle to the side of the A48, while the van did not stop, said South Wales Police.
A 59-year-old man from the Cowbridge area was arrested later.
Mr Richardson, awarded an MBE after two golds and a silver at the 2008 Beijing games, was flown to hospital.
Two cars were then involved in a crash at the same location, with an elderly motorist released after treatment in hospital.
Police have appealed for witnesses after the crash at 09:40 BST on Wednesday outside Crack Hill House, Bridgend.
Police said Mr Richardson was apparently struck by a small white van travelling in the same direction, which did not stop and continued east towards Cowbridge.
A black Toyota Avensis estate, driven by a 43-year old man, and a gold Rover 25 driven by a 74-year-old woman were then also in collision at the same place.
The ambulance service treated both Mr Richardson and the female driver.
He was flown by air ambulance to University of Wales Hospital, Cardiff where he is undergoing treatment for multiple injuries.
The female motorist was released after treatment for chest injuries.
South Wales Police would like to speak to any person who witnessed the collision, or may have been travelling between Cowbridge and Bridgend on the A48 and saw a white small van leaving the area.
They also want to speak to anyone who stopped to provide assistance and who has not yet given their details.
The road was closed for four hours while the police conducted initial investigations.
Mr Richardson, from Porthcawl, had been seriously injured in a cycling incident with a car in 2001 while out with friends from a cycling club.
He received the MBE in 2009.
He won Britain's first gold at Beijing in the LC3/4 1km time trial in world record time.
One of Mr Richardson's sponsors is Phil Jones, of Brother UK.
He said he spoke to Mrs Richardson shortly after the incident and she told him her husband was "critical but stable".
Mr Richardson had been diagnosed with multiple fractures of the spine, a broken pelvis and a broken breast bone and only one of his lungs was functioning, he said.
Mr Jones told BBC Wales: "There is quite a big community of people who know Simon and know of his achievement. There's a real sense of support for Simon."
He added that the full-time athlete was shortly due to test a new time-trial bike as part of his training to qualify for the London 2012 Paralympic Games.
Gerwyn Owen, of Disability Sport Wales, said the incident highlighted the need for everybody to look after cyclists on the road and for cyclists to take care themselves.
"This happens very often in cycling," he said.