Born in London in 2003 to a Danish-German father and a Bosnian mother, Biereth was, in addition to Denmark, also eligible to play for Bosnia, Germany, and England.
Bayern Munich's Musiala, who was one of the stars for Die Mannschaft during the Euros last summer, was keen to persuade Biereth to play for Germany.
"I have spoken to him, and he would have liked me to have chosen Germany," Biereth told TV 2 Sport.
"But in my heart I have always wanted to play for Denmark, and I am happy that I have come here. I hope that I can play a few minutes and become a real (senior) national team player."
"Our families are close, so he knows that I am also German. He speaks German with my father, and he is not too happy with (my choice). But I am satisfied and I am looking forward to it."
Musiala had a similar choice to make earlier in his career and, after representing England in several youth teams leading up to the U21s, he chose to play for Germany.
Biereth, who has scored 11 goals for Monaco this season, is likely to get his debut for Denmark in the Nations League quarter-final clashes against Portugal on 20th and 23rd of march.