A spokesman for Warwickshire Police and West Mercia Police said officers were called to the farm in Stanton upon Hine Heath, Shropshire, on Friday April 8 at 6.48pm.
It is believed the man was attempting to pull out a tractor and drill which had become stuck in a field.
The police spokesman said: “A man sustained serious head injuries and was airlifted to hospital for treatment.
“The Health and Safety Executive have been informed and will be leading on the investigation.”
A member of The Farming Forum said the incident served as a stark reminder of the dangers of using chains to tow machinery.
“I post this only as a warning that chains aren’t man enough for these machines," he wrote on the online forum.
“I believe that all the local farms have now scrapped their tow chains and replaced with 30 ton straps.
“Our thoughts are with his family and fellow workers traumatised by the accident.”