British sprinter Dwain Chambers will have to wait until next year before he can return to the track.
Chambers considered a career in American Football
The 27-year-old was expected to return from his two-year ban on 8 November.
But under World Anti-Doping Agency (Wada) rules, Chambers must pass three mandatory drugs tests before he is allowed to compete again.
"The actual date he'll be eligible can't be specified at this time but it's anticipated it will be in early 2006," read a UK Athletics statement.
There must be a minimum of four months between each test, although the random element of the procedure means the gap can be longer.
Chambers received the two-year ban back in November 2003 after testing positive for steroid THG.
Chambers had the first of the tests in March this year and the second in August, meaning the earliest his third test could take place would be in December.
After the third test, Chambers must then undergo one final test - although there is no requirement for a four-month gap - before finally being cleared to compete.
Chambers, who is co-operating fully with the reinstatement process, had considered a career in American Football but was forced to return to the UK when his visa expired.
"Following his ban, Dwain considered a future outside of the sport and was removed from the anti-doping register at his request," continued the statement.
"In March this year he requested that he be placed back on the register and for the reinstatement process to begin.
"This delay in the start of his reinstatement procedure means that he will not be clear to compete from 8 November."
UKA's athletics performance director Dave Collins said: "We are aware of the circumstances regarding Dwain's return from the ban.
"It is essential that these procedures are followed to the letter of the law.
"Dwain knows this and is co-operating with anti-doping to ensure that there is no further delay."