LIVERPOOL, England — Whenever one of Real Madrid’s galaxy of stars is injured, one of the first people the club’s medical staff contacts is usually Terry Nelson.

Nelson is many things — inventor and entrepreneur, amputee and erstwhile athlete — but he is not a doctor or a surgeon. Regardless, Real Madrid’s in-house physicians tend to get in touch with him almost as soon as a player is sidelined. Often, they will apprise Nelson of their plans for the player’s rehabilitation. Sometimes they just seek his counsel. He makes an unlikely first port of call for the most powerful club in the world, but then everything about Nelson’s story is unlikely, and it is only getting started.

Nelson, 55, is known to Real Madrid as the creator and designer of what its former manager José Mourinho used to call the club’s “secret weapon,” a buoyancy suit that is used primarily to help injured players train in water, enabling them to build their fitness when they are unable to run normally.

He first sold his suits, made from Lycra, nylon and foam padding, to the club in 2012. After a single demonstration at the club’s training facility at Valdebebas, Real’s medical department ordered 50 on the spot. They now form a core part of Madrid players’ recovery work.