In 2017, the UAE accused Qatar of sabotaging security in the region by funding terror groups and has since made any form of support for Qatar a major offence.
Amer Loki, a friend of Ahmad who was able to speak briefly to him on the phone last week, told the Guardian that he had grave fears for his friend's safety.
"He didn't sound good when he spoke to me on the phone. He was speaking very slowly and he sounded very frightened," Loki said. "He begged us to do whatever we can to get him released so we contacted the Foreign Office and asked them to help get him released.
"He said he would call us back but since then we have not heard anything from him. I am in shock that he was arrested and assaulted because of the football T-shirt he was wearing. We are all so worried about him. This is very serious."
The UAE embassy told the Guardian that it was investigating the circumstances of Ahmad's arrest and the Foreign Office was offering support.
"The United Arab Emirates embassy is looking into allegations that a British citizen has been detained. The UAE is a nation built on the rule of law and respect for individuals. We take any allegation of human rights violations extremely seriously – whether it concerns one of our citizens or any of the 1.5 million Britons who visit us each year," a UAE spokesperson said.
An FCO spokesperson confirmed that they were "providing assistance" to a British man arrested in the UAE and were in touch with the local authorities.