Tony Callen flew over the handlebars when his front wheel wedged itself perfectly into a crack.
Mr Callen then had to frantically wrestle his bike off the level crossing before a train came.
He says Network Rail should fix the problem before a serious accident occurs at the crossing in Inlands Road, Nutbourne, near Emsworth.
The 71-year-old retired lecturer, who suffered injuries after landing on his face, said: 'We were riding along the road when suddenly I found myself on my face. The front wheel of the bike had simply gone down a hole in the road.
'Luckily, I had a friend with me to help, but what if someone was alone and knocked unconscious? Roads are not designed to have slits that take bikes down with them.
'My helmet basically saved me. I was very lucky.'
Mr Callen, of Second Avenue, Havant, suffered a severed lip and a cut to his nose and fears he may be permanently scarred.
The police were contacted about the accident on June 8 by Mr Callen, but, a month on, nothing has been done to rectify the problem. Mr Callen said: 'It just shouldn't be there – and it could kill someone.'
Gary Gaskarth, spokesman for Network Rail, said the tracks are inspected every six months. He added: 'When the concrete slabs between the rails are laid, there are no spaces between them.
'However, there are some factors, such as vibrations from train movements, which can cause small gaps to form.
'This sort of thing is picked up in the regular inspections we carry out on all our level crossings, but unfortunately the gap at Inlands Road level crossing appears to have formed between inspections.
'We will take action to close the gap as soon as possible and apologise to Mr Callen for any distress caused by this accident.'
SAFETY CAMPAIGNNetwork Rail is currently investing in a new campaign called Don't Run The Risk to educate members of the public about using level crossings safely.
There are around 7,000 level crossings in active use in the country. Of these around 1,500 are on public vehicular roads and the remainder are where public footpaths, bridleways and private roads or tracks cross the railway.
On average there are seven pedestrian and two to three driver or passenger fatalities per year – excluding suicides. Accidents involving injury to persons on the train are rare.
>> Vote in our latest web poll.