He fell from a first-floor balcony at his home in Nyahururu, and a police investigation is underway.
The 24-year-old won in Beijing in 2008 in an Olympic record time, becoming Kenya's first marathon champion.
His sporting victories include the Chicago and London marathons.
Last December, he was charged with threatening to kill his wife, Triza Njeri, assault and the illegal possession of an AK-47 assault rifle.
Mrs Njeri subsequently withdrew her accusations, saying they had reconciled. He was due to appear before a court on 23 May on the charge of illegal possession of a firearm.