Outstanding for Rangers since joining this season on-loan from Tottenham, teenage Moore missed six weeks last season.
He has now admitted he was suffering from myocarditis.
Speaking in a video shared on Tottenham’s official website, he recounted: “I was playing really well, starting to find my feet in the first team, then I think it was just before the Galatasaray game.
“I trained a couple of days before it, I think I was set to start or make an appearance in that game, then went for a driving lesson that night and all of a sudden I just felt a pain in my chest.
“The doctor called me and just said ‘forget about football for now’. It came back that i had myocarditis, which is a virus and it went to my heart, gave me the pain in my heart.
“I’m lucky I caught it early because I’m not sure what could have happened after that. I think I was in bed for six weeks. I wasn’t allowed any exercise.”
Moore added that the illness is not expected to recur, according to specialists.
He also said, “There was a lot of rumours at that time and it was tough to deal with. That six weeks was not six weeks of improving in the gym like with a usual injury.
“Right now, I feel at my best. I feel kind of what I felt like when I first started playing at Tottenham. That’s all done now. Put it behind me. That’s it, really.”