With ten goals in eight games Biereth has made a splash for himself in the French Ligue 1, when he wiped out Zlatan Ibrahimovic's previous goalscoring record.
Born in London in 2003 to a Danish-German father and a Bosnian mother meant that Biereth is in fact eligible to play for Denmark, Bosnia, Germany, and England.
Nagelsmann was also asked about Mika Biereth and the possibility of including him in the German squad on Thursday's press conference.
"I spoke to him to see if he could play for us. He has a Danish and a British passport, and was 21 years old the last time he represented Denmark (on the U21 national team, ed.)."
"Therefore it was not legal for him to line up for Germany", said Nagelsmann.
Biereth was instead included in the Danish squad for the upcoming fixtures against Portugal.