Nasri, 31, was suspended from playing football for eighteen months by anti-doping agency WADA until January 2019 following a doping violation.
The former France international has since returned to the Premier League with West Ham United - following the ban and instantly slotted in as a key part of manager Manuel Pellegrini's plans.
However, the former Premier League winner has broken silence to L’Équipe on the events that led to, what he thought was the end of his career.
"I was on holiday with my family. I became ill, I had a virus. I did not leave my rooms, I was suffering from vomiting, big headaches, I was empty. I called a friend and told him to find me a doctor. He couldn’t. He said to me: 'there is a clinic, it will re-boost you'. Especially as I was going back to Sevilla in two days time," the former France international revealed.
"I said ok. I didn’t know the rules. And that by the way, should serve as a lesson to all young players, to properly read the anti-doping rules, to really pay attention because everything can go in a completely different direction. To be honest, I did not think that anything would come of it.
"This woman came to give me a drip of vitamins. She asked for a photo, I said yes, for me I hadn’t done anything wrong. I was of the view that this was not a doping product, it was fine.
"Can I promise that I have never doped? Yes, I have handed over the files, there was no doping product in it."