Alex Dowsett's attempt on the hour record is in doubt after the Englishman broke his collarbone while training.
The 26-year-old is due to try to beat 51.852km - set by Matthias Brandle in October - at the London Olympic Velodrome on 27 February.
The Commonwealth Games time trial champion will have surgery on Thursday.
"Details on whether his attempt will go on as planned or be postponed will be specified in the next few days," said his Movistar team.
Australians Jack Bobridge and Rohan Dennis will make their own bids to beat Brandle's mark on 31 January and 8 February respectively.