England's Alex Dowsett has postponed his attempt to break the hour record after a slower than expected start to his recovery from a broken collarbone.
The 26-year-old had been due to try to beat 51.852km - set by Matthias Brandle in October - at the London Olympic Velodrome on 27 February.
"I'm really gutted," said Dowsett. "I've never worked harder for anything and to lose this opportunity is a blow.
"The positive is that we will be attempting it at a later date."
Dowsett's Movistar team said attempting the record before he was properly prepared could compromise the rest of his season.
"I'll now recover properly and be back to full fitness for the road season and another crack at the 'perfect hour'," added the 2014 Commonwealth Games time trial champion.
Australians Jack Bobridge and Rohan Dennis will make their own bids to beat Brandle's mark on 31 January and 8 February respectively.
Sir Bradley Wiggins has also expressed an interest in taking on the challenge in 2015, although a date is yet to be set for his attempt.
Dame Sarah Storey is due to attempt the women's hour record at the London Olympic velodrome on 28 February.