Six-time Olympic cycling champion Chris Hoy revealed Friday he has been diagnosed with cancer but insisted he was "optimistic and positive" over the future.

The 47-year-old former track racer said he is currently undergoing treatment, including chemotherapy, adding it is "going really well" and that he feels "fine" at present.

Hoy, writing on his Instagram account, said: "Last year I was diagnosed with cancer, which came as a huge shock, having had no symptoms up to that point.

"I'm currently receiving treatment including chemotherapy, which thankfully is going really well. I'd like to extend my sincere gratitude to all the medical professionals for their amazing help and care."

The Scot added he had wanted to keep his condition private but explained his "hand has been forced" as he looked forward to an "exciting year of work ahead" that includes the Olympic Games in Paris.

"I'm optimistic, positive and surrounded by love for which I'm truly grateful. As you might imagine, the last few months have been incredibly difficult. However, I currently feel fine -- I am continuing to work, ride my bike and live my life as normal."

Edinburgh-born Hoy took up track cycling as a teenager and won his first Olympic medal, a team sprint silver, at the 2000 Games in Sydney.

Four years later, he became an Olympic champion by winning the one kilometre time-trial in Athens.

He increased his Olympic medal haul with three more golds at the 2008 Games in Beijing and another two at London 2012.

Hoy also won 11 world titles before retiring from competitive cycling in 2013.