Vinod Nargund, a surgeon from St Bartholomew's Hospital in London, said that cycling restricts blood flow and generates excessive heat. This could result in men having difficulty with erections.
Cycling puts pressure on the nerves which can also affect a man's sperm.
More than 60 per cent of male cyclists experience genital numbness, according to Mr Nargund, a urology consultant.
He said: "The bicycle saddle makes contact where the nerves and blood vessels enter the back of the scrotum and penis.
"Numbness is common because the pressure of the saddle can impair the blood supply to this area. This can also affect the man's ability to get an erection."
Mountain bikers run a particular risk, as do those riding with too much pedal resistance.
Mr Nargund did not establish a clear link between cycling and male infertility, but said it is recognised as a possible side effect.
Cyclists must choose the right bike to avoid sexual problems, while a padded saddle and shorts are essential, he said.
"The male cyclist should know his bicycle well. An appropriate frame should be selected and adjustments made considering posture, height and balance," Mr Nargund said.
Regular rest periods and cycling in a lower gear are also advised in the article, published in the online urology journal BJU International.
