Becky James has suffered a setback in her recovery from a serious knee injury, says British Cycling chief Shane Sutton.
The former double world champion, 23, missed the 2014 Commonwealth Games due to recurring trouble in her left knee.
She also underwent surgery on a long-standing shoulder problem but Sutton said the knee injury was still a cause for concern.
"Becky has had a few setbacks over the last week or so," he said.
"We looked like getting her back in the spring but there have been one or two little complications.
"I have no detailed report. That is kept between the doctors, medical team and her rehab team.
"They are doing a great job and she is getting the best treatment possible."
James aggravated the knee injury when she returned to training following a period of rest after a minor medical procedure.
The Abergavenny-born track cyclist won silver and bronze for Wales at the Commonwealth Games in 2010, but came to international prominence at the 2013 Track World Championships.
She won golds in the keirin and sprint and also picked up bronze medals in the team sprint and 500m time trial in Minsk.
James missed out on the London Olympics in 2012 after a season wrecked by injury and illness, but Australian Sutton has no doubt that success at Rio 2016 remains realistic.
"I am totally confident we will get her right for Rio," Sutton added.
"Another four or five weeks is really not going to matter. She has lost a lot of time but give us 12 months and a clean bill of health, then Becky will be knocking them over in Rio.
"We are talking about a girl that is one of the best on the world stage.
"If anyone is going to survive this and cope mentally, it will be Becky."