Extreme obesity may in future be classified as a disability under EU law, providing protection for morbidly overweight workers who suffer discrimination at work.

The advocate general of the European court of justice (ECJ) in Luxembourg issued a preliminary ruling on a claim by Karsten Kaltoft, a Danish childminder who was dismissed by his local city council in 2010 after reportedly being unable to bend down to tie up shoelaces. The court heard that he weighed more than 160kg (25st).

An advocate general's opinion is not binding but is usually followed by the court, whose judgments have force across the whole of the European Union. UK courts have not yet recognised obesity as a disability.

Kaltoft argued that his weight was one of the reasons he lost his job and that it amounted to unfair discrimination. His employer, Billund city council, disputed the allegation.

The ECJ was asked to rule on whether EU law forbade discrimination on the grounds of obesity and whether obesity could be considered a disability. The advocate general, Niilo Jaaskinen, who advises the court, found that EU law did not prohibit discrimination specifically on the grounds of obesity, but concluded that very severe obesity – classified as a body mass index (BMI) of more than 40 – could be considered a disability.

"If obesity has reached such a degree that it plainly hinders participation in professional life, then this can be a disability," Jaaskinen said.

Kaltoft never weighed less than 160kg during his employment and had a BMI of 54, the advocate general said.

Jaaskinen threw out the notion that a self-inflicted disability could be any less worthy of protection, saying: "The origin of the disability is irrelevant. [It] does not depend on whether the applicant has contributed causally to the acquisition of his disability through 'self-inflicted' excessive energy intake."

The ECJ will now consider the Kaltoft case in greater detail. If it upholds Jaaskinen's view, it will be up to a Danish court to decide whether Kaltoft's obesity met the court's definition of a disability.

If successful, Kaltoft's case could force widespread changes in the way employers deal with staff and what support – for example, reserved parking – they might be required to provide.

Glenn Hayes, an employment partner at the UK law firm Irwin Mitchell, said: "This could mean that employers could find themselves under a legal obligation to make adjustments such as providing car park spaces close to the workplace entrance for obese employees, providing special desks, or providing duties which involve reduced walking or travelling, or possibly even ensuring that healthy meal options are provided at their staff canteen."

Richie Alder, an employment partner at the law firm Trowers & Hamlins, said: "Employers do need to be aware that 'extreme, severe or morbid' obesity may, in fact, be classified as a disability if it affects participation in professional life, and in these cases reasonable adjustments may need to be made."

Nicola Rabson, of Linklaters law firm, said: "This decision shifts the burden of keeping those who are severely obese in the workforce to employers, who must make adjustments to accommodate any special requirements arising from a person's disability. Obesity, particularly severe obesity, can be a sensitive subject, so employers will have to tread carefully and not make assumptions about the needs of an obese worker."

In the USA, several recent cases have resulted in dismissed workers winning claims that they were discriminated against for being obese. In one case, a worker in Texas who weighed more than 305kg received $55,000 (£32,800) in compensation for losing his job.