A French appeals court has said US chemicals giant Monsanto was guilty of poisoning a farmer who said he suffered neurological damage after accidentally inhaling fumes from a weedkiller made by the company.

Paul François, a cereal farmer, had already won previous lawsuits against Monsanto, which was bought by Germany’s Bayer last year, in 2012 and 2015.

He said he fell ill in 2004 after being exposed to Lasso, a weedkiller containing monochlorobenzene that was legal in France until 2007 but had already been banned in 1985 in Canada and in 1992 in Belgium and Britain.

François argued that Monsanto was aware of Lasso’s dangers long before it was withdrawn from the French market and sought damages of more than €1m (£860,000) for chronic neurological damage that led to long hospital stays.

The court in Lyon rejected the company’s appeal on Tuesday but did not rule on how much Monsanto might have to pay, which will be determined in a separate ruling. It ordered the company to pay €50,000 immediately for François’s legal fees.

In its ruling, the court found that Monsanto should have clearly indicated on Lasso’s labelling and instructions for use “a notice on the specific dangers of using the product in vats and reservoirs”.

“The plaintiff’s assumed technical knowledge does not excuse the lack of information on the product and its harmful effects – a farmer is not a chemist,” it added.

Speaking after the verdict, a lawyer for Monsanto France, Jean-Daniel Bretzner, said the company would probably appeal, since the ruling applied to Lasso’s producer – in this case, Monsanto Europe.

It was the latest judgment against Monsanto involving its weedkillers and pesticides, which have been widely used around the world for years.

Last month, a San Francisco court ordered the company to pay about $80m to a retiree who blames its popular Roundup weedkiller, which contains glyphosate, for causing his non-Hodgkin’s lymphoma.

The company said it would appeal, as it faces thousands of similar lawsuits in the US.

Monsanto denies that the weedkiller causes cancer and has challenged findings by the International Agency for Research on Cancer, an arm of the World Health Organization, which classified glyphosate as a “probable carcinogen” in 2015.