It is thought that Forest turned down an offer of about 18 million pounds from the Bees for Brennan Johnson.
The 20-year-old Wales forward has played 33 games this season and has seven goals.
He has become a first-team regular this season after a loan spell at Lincoln City in 2020.
The only January signing so far is Lossl.
The option to make the move permanent was available to the Danes when they arrived on loan.
Derby County have been charged with failing to ensure their players conducted themselves in an orderly fashion after the game.
There were incidents at the end of the game, which Forest won, and after the final whistle.