Alex Dowsett's attempt to break the hour record appears to be in doubt after he suffered a broken collarbone.
The English rider is due to try to better Matthias Brandle's effort over 60 minutes at the London Olympic Velodrome on February 27, but the injury suffered in training could see his attempt pushed back.
The 26-year-old, who won time trial gold at last year's Commonwealth Games, will undergo surgery on Thursday, with his Movistar team revealing that a decision on his participation will be made in the coming days.
Since Ondrej Sosenka's long-standing time was beaten by Jens Voigt in September the record has proven popular with cyclists, with the German's time topping the list for just a month before Brandle set a new mark.
Former Tour de France winner Sir Bradley Wiggins has previously signalled his intent to try to break the record at some point during 2015.
