Pro-Mil Engineering, of Bodymoor Heath Lane, Bodymoor Heath, was fined £5,000 and ordered to pay costs of £3,314 at Nuneaton Magistrates' Court on 28 July.
The Health & Safety Executive (HSE) prosecuted the firm after the 42-year-old employee, who had no arboriculture training, was struck on the head by a falling log.
The court heard that the incident on 24 July 2007 at the company premises occurred during the removal of a willow tree that was leaning over the boundary fence. The tree was pulled in the opposite direction using a rope and a forklift truck to avoid damaging the fence.
HSE investigating inspector Neil Craig said: "Neither the injured man nor any of his colleagues who assisted had been formally trained for any aspect of the task or held a relevant certificate of competence in the use of chainsaws for felling trees. They were simply asked to assist during a break in their normal work."
As the tree was felled, the trunk twisted, putting tension on the rope and releasing the log to catapult across the yard, striking the employee on the side of the head.
Pro-Mil pleaded guilty to breaching section 2(1) of the Health & Safety at Work Act 1974.
"As a result of the company's failure to take basic precautions, a man suffered severe head injuries, which were initially considered to be life-threatening, and his colleagues were also put at risk," added Craig.
Pro-Mil managing director Mike Hedley declined to comment.
Arboricultural Association technical officer Simon Richmond said: "Tree felling is a high-risk activity and the level of expertise required is often underestimated.
"People think they can attack these kinds of jobs but can quite easily get into difficulty."