Council officials have pledged to leave 'no stone unturned' in finding out how a young boy was injured in a tree felling accident.
Four-year-old Oliver Rollinson, from Dinnington, was hit by the tree while walking on a footpath in Deepcarr with sister Ava, aged five, and grandmother Zena Crawshaw on Monday.
He needed surgery to a deep cut on his cheek while Miss Crawshaw, from Deepcar, also required hospital treatment for a wound to her head.
Trees close to the path were being felled by a contractor, Sheffield Landscape Trust, on behalf of Sheffield Council during site clearance work for the new Upper Don Valley cycle link.
A Sheffield Council spokesman said: "We are really upset to be informed of this situation.
"Our thoughts are with Oliver and his family and we wish him a full and speedy recovery.
"We have been in touch with his family and will continue to talk with them."
Investigations into the incident have been launched by the council and the Health and Safety Executive.
The spokesman added: "We are taking this extremely seriously and have launched an immediate investigation with our own health and safety team.
"The Health and Safety Executive has also visited the site and is investigating the matter.
“There will be a full investigation, which will leave no stone unturned in finding out precisely what happened and how we can ensure it never happens again.”
A HSE spokesman said: “HSE is aware of the incident and making initial enquiries”
Sheffield Landscape Trust has been approached for a comment.