Mo Farah is consulting lawyers after a vape company appeared to use a lookalike to promote e-cigarettes.
Banners advertising Diamond Mist menthol e-liquid were seen on London buses with the slogan “Mo’s mad for menthol”.
The motto appeared on blue banners with a photo of a man with a bald head and thick eyebrows - who could be mistaken for the four-time Olympic champion.
Sir Mo's representatives have said they are thinking about taking legal action against Diamond Mist, a leading supplier of vaping equipment and e-liquids, which contain nicotine.
Sir Mo, who promotes healthy living and has his own range of health and fitness products, had no involvement with the company and does not endorse its products.
Agent Jo Livingston said the long distance medallist "has nothing to do with this company" and "or course he does not vape."
She said: "I can confirm that Sir Mo Farah has no relationship with this company and has absolutely not endorsed this product.
"Of course he does not vape - as if he would ever endorse e-cigarettes or vaping.
"We became aware of the advert last week. We have just passed it onto our lawyers because we believe people could think it is Mo but it is clearly not. He has nothing to do with this company.
"Clearly it is not in our interest for people to think Mo would ever be endorsing such products."
'It is compliant'
Diamond Mist said that the vape company ran five adverts within the series - each containing a different name for each flavour such as "Claire’s Crazy for Cola".
In a statement, Diamond Mist said: "The aim of the campaign it to feature a diverse range of people to reflect the diversity of London and the wide range of people who use our products.
"At no point was there any intention to associate out Menthol product with Sir Mo Farah. The original image of the model, that shows the full face, bares no resemblance to Sir Mo Farah.
"Mo is an extremely common name and we imagine there are several people who might think this advert could resemble them.
"In the same way there is probably somebody with the name ’Claire’ who resembles the person used in the Cola advert."
The Advertising Standards Agency declined to comment as no formal complaints had yet been made.
The Diamond Mist adverts can be found across 100 London buses and promote the brand's variety of e-liquid vape flavours - including "Mo's" menthol.
A TfL spokesperson said: "We are not sure if it is supposed to be Mo Farah or not - there were mixed opinions.
"They have other adverts for other names of people and names of flavours.
"We did seek advice about the 'Mo's mad for menthol' slogan from CAP and they have said that was compliant and it is compliant with our policy.”
Diamond Mist has been contacted for comment.