St Edmundsbury Borough Council has pinned a notice to a horse chestnut tree saying "Beware Falling Conkers" after a passer-by was hit on the head.
Officials said the warning note, attached to a tree in Abbey Gardens in Bury St Edmunds advised walkers to "proceed with care''.
A spokeswoman for St Edmundsbury Borough Council said the notice was put up in the Abbey Gardens earlier this week as a "courtesy'' to visitors and would stay until all conkers had fallen.
She said a walker suffered a cut head after being hit by a falling conker and parks staff had decided to issue a warning.
"A couple of people came into our parks office after one had been hit by falling conkers and asked if we could warn people at this time of year,'' said the spokeswoman.
So, as a courtesy to our many Abbey Gardens visitors, we have put up a temporary notice.
The notice will stay there until the conkers have fallen to the ground - and they are then free to be used by children, or indeed visitors of any age, as they always have done for conker contests or similar autumn pastimes."
She said the council did not have a "a health and safety policy about conkers'' and did not have warning signs on any other trees.