Mark Cavendish suffered a collapsed lung and two broken ribs in a crash during the Ghent Six Day track event on Sunday night, his Deceuninck-QuickStep team announced.
Cavendish spent the night in the intensive care unit of a Belgian hospital after leaving the velodrome on a stretcher, but is expected to be discharged soon.
A statement said: "Following his crash at the Ghent Six Day, Mark Cavendish was taken to the Ghent University Hospital where he was kept overnight.
"Examinations showed that Mark has suffered two broken ribs on this left side and has a small pneumothorax, both of which have been treated with medication and he has been kept in the hospital for observation.
"It is expected that Mark will be discharged either later today or tomorrow morning, and will then undergo a period of recuperation. Everybody at Deceuninck-QuickStep wishes Mark a speedy recovery."
Cavendish, who was racing in the event alongside team-mate Iljo Keisse, was one of several riders to crash in the final race. The 36-year-old stood and waved to spectators following the incident, but was then put on a stretcher and taken to hospital.
His wife Peta Todd posted on Twitter: "Thank you for all the messages. Mark is spending the night in ICU following today's crash. Thank you to all the medical staff that helped us today and also to the staff that sprung into action to help me and the kids."
In an interview with the Times prior to the crash, Cavendish had described racing on Ghent’s 166-metre velodrome, shorter and steeper than the Olympic standard 250m, as like being on a "wall of death", admitting he was "petrified of it" following a crash two years ago.
However, the three-time Madison world champion remains keen on track racing, and was using the event to bring down the curtain on a year which he has described as a "fairytale".
Having feared his career was over last year, Cavendish signed a minimum-wage contract with Deceuninck-QuickStep and then used an unexpected late call-up to the Tour de France to win four stages, his first since 2016 as he matched Eddy Merckx’s all-time record of 34 victories in the race.
Cavendish is expected to sign a new one-year deal with the Belgian outfit, with talks continuing.
Ireland's Tour de France green jersey winner Sam Bennett was a member of the team for two years, but will rejoin Bora-Hansgrohe in 2022 following a summer of inflammatory comments from team manager Patrick Lefevere after he suffered a season-ending knee injury.