Triple road race world champion Peter Sagan requires heart surgery which could endanger his bid to qualify for late July's Paris Olympics mountain bike race.

Sagan, 34, was reported to have undergone a first operation recently.

He has now said on Instagram that "while I was training on the rocky trails in Marseille, my heart hit a few bumps.

"Nothing to worry about, you could say that my heart needs a pit stop.

"I will undergo surgery next week and thanks to my friend, sports cardiologist Dr Roberto Corsetti, I am sure I will be back in the saddle very soon," he said.

Sagan ended his road race career last year, winning three straight world titles (2015-2017), 12 Tour de France stages and also stages at the other two grand tours, the Giro d'Italia and Vuelta a Espana.

He has competed in mountain bike before, including at the 2016 Olympics.