Defending champion Mark Cavendish has pulled out of Sunday's National Championships road race in Wales because he has bronchitis.
The Manxman, 28, won the title in Glasgow last year.
Cavendish said: "I'm sad because, as current champion, I would really like to defend the title."
The Omega Pharma rider added that he was focusing on being ready for the Tour de France, which starts in Yorkshire on 5 July.
"I think it's wiser to not take any risks and focus on absolute, 100% recovery, and continue to train for the Tour de France," added the former world champion.
The time trials will take place in Abergavenny on Thursday, with the road races being held on Sunday.
Team Sky's 2012 Tour de France winner Sir Bradley Wiggins will take part in the senior men's race.