Werner has been heavily linked with a move away from Leipzig at the end of the season, with reports stating the forward has a €60 million (£53m/$65m) release clause in the contract he signed in 2019.
Bayern, Manchester United and Liverpool are the sides who have been credited with the most interest in the 24-year-old Germany international, who has scored 30 goals in all competitions for Leipzig this season.
Nagelsmann has made clear his intention to keep Werner, though he acknowledged the call will ultimately not be down to Leipzig, who looked set to challenge for the Bundesliga title this season until their form dipped after the winter break.
And the former Hoffenheim coach did not shy away from explaining how big of a loss Werner would be, should he leave.
"Of course you have conversations from time to time, but I have not spoken to him about that in the recent past," Nagelsmann told a news conference ahead of Leipzig's clash with Cologne.
"I think he now has 34 goals and assists [this season]. I think you have to mention that I would like to keep him. That is an extraordinary quality.
"If he leaves for the next season there would be a big gap. It's like if Robert Lewandowski leaves Bayern Munich. Nobody shouts 'Hurray!' there either, I think. They're clearly weakened then, and it's the same with us.
"That we'd like to keep him is completely normal. He has an exit clause until a certain date - I honestly don't know when - and if a club comes along and he agrees with them by then, then that's the way it is."
Nagelsmann has little else to say to Werner when it comes to making an attempt to get the forward to stay put.
"There is nothing we can do about it anyway. He knows what he has in Leipzig and also what he has with me, I know what I have in him," Nagelsmann said.
"And I show him that - similar to what I do with [Dayot] Upamecano - by letting him play every game from the beginning and if everything goes normally he is allowed to play through most games.
"He gets many chances to develop himself. That's my job, I have to do that. I don't know if it will help him that much if I tell him every day. I try to do it more with action.
"A player has to feel that he can get better. If he doesn't feel that, it wouldn't do any good if I kept on telling him to stay here. In the end it is his life, his career, he can decide that.
"We already had this discussion last year, then in winter and now again. I'm basically someone who knows what he has to say and can add his two cents to everything.
"But here I can't think of anything new to say to Timo either. So I rather try to convince him with actions and in the end he has to know what he wants to do."