Nelson is expected to sign a new deal this morning before moving to Hoffenheim ahead of tonight's market deadline.
Nagelsmann enthused: "We are interested, I can say that openly. There are final details to clarify.
"Reiss has similar traits as Serge (Gnabry) - which is his one-on-one and his pace. These are components that we do not have much in the squad. It was my wish that we refill there again.
"He can actually do everything on the ball. Of course he does not have the experience yet. But I love developing players.
"Nelson can play central, offensive and both wide positions.
"We will give him the time.