The striker is hot property on the transfer market, with interest from Liverpool, Manchester United and Chelsea.
He scored 31 goals with 12 assists in 40 competitive games for RB Leipzig so far this season, but the clause worth €60m expires on June 15.
“There is nothing we can do about it. He knows what he has in Leipzig and also what he has with me,” said coach Nagelsmann.
“He gets many chances to develop himself. I don’t know if it will help him that much if I tell him every day. 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. I can’t think of anything new to say to Timo.”