Martyn Irvine will be out of action for about five or six weeks after suffering a hip fracture in a crash in Belgium on Wednesday.
The Northern Irishman, 31, was competing in the Baloise Belgium Tour event for his Irish professional team Aqua Blue Sport.
Former world track champion Irvine came out of retirement last October to sign for the team.
A team tweet said Irvine had sustained a “minor hairline fracture”.
Irvine’s team-mates include fellow Irishmen Matt Brammeier and Conor Dunne.
The County Down man retired from the sport after failing to qualify for the Rio Olympics before reversing the decision nine months later.
Aqua Blue Sport’s goal is to eventually participate at a World Tour level and compete in the Tour de France, but their events this season include the Milan-San Remo classic, Amstel Gold and the Tour of Britain.
Newtownards man Irvine became the first Irish cyclist to win a world track title in 117 years with victory in the scratch race in Belarus in 2013.
Irvine also won silver in the points race at the 2013 World Championships and a European bronze medal
He finished 2013 as number one scratch rider in the 2013 UCI world rankings and claimed a scratch silver medal in the 2014 Track Cycling World Championships.
His achievements in 2013 led to him being named as the BBC Northern Ireland Sports Personality of the Year.