“Can you tell my friend to stop taking pictures of you please,” they wrote, adding three laughing emojis.
Gymnation is a gym in Dubai, where the 24-year-old currently lives.
Gill, who won the 2019 of summer Love Island alongside rugby player Greg O’Shea, said the comment had made her feel extremely uncomfortable.
“I dunno why you’re putting laughing faces that’s super, super embarrassing. I would be highly embarrassed to be friends with such a loser,” she replied to the Instagram user, as reported by The Sun.
“This is actually severe bad vibes. So, whoever is doing that stop you f**king creep. And now I will have to change gyms. F**king weirdos.”
She also tagged Gymnation in the exchange, asking the gym if someone was allowed to photograph other people in the gym.
In a later Instagram story, Gill said the incident had made her cry.
“Sorry I was going to continue answering questions but that has genuinely threw me off and made me feel soooo uncomfortable. I even shed a tear,” she wrote.
“I always train in the ladies only section and come to the main gym and men have to ruin it. Call me misandrist.”
The news comes less than a week after Gill was reprimanded by the Advertising Standards Agency (ASA) for failing to disclose adverts on her Instagram despite repeated warnings.
The ASA said Gill had been contacted by its compliance team and asked to “provide assurance” that she would include “clear and upfront” ad labels when promoting products on her social media accounts.
Gill had either failed to respond, or continued to post adverts without full disclosure and will now be subject to a period of enhanced monitoring, the ASA added.
The Independent has contacted Gymnation for comment.