Upamecano and Hernandez are two of the nine Bayern players who were sidelined by the virus at the start of January and Nagelsmann believes the Frenchmen will make their first appearances of 2022 on Sunday.
That would free up Germany’s Joshua Kimmich to move from right-back, where he has played the last two games, to defensive midfield.
Nagelsmann said “if everything goes to plan” with Hernandez and Upamecano, fellow Frenchman Benjamin Pavard will move from centre-back “to the right”.
League leaders Bayern start the weekend with a six-point cushion in the Bundesliga over second-placed Borussia Dortmund, who are away to Hoffenheim on Saturday.
Hernandez is set to slot in at left-back for Alphonso Davies, who is still recovering from a slight inflammation of the heart having had Covid-19.
“‘Luci’ (Hernandez) defends well down the left and is more of a passer, but of course he is different in attack compared to ‘Phonzy’ (Davies), who brings more tempo,” Nagelsmann said.
Bayern are still missing several players with Cameroon striker Eric Maxim Choupo-Moting and Senegal defender Bouna Sarr both at the Africa Cup of Nations.
Injuries continue to sideline both Josip Stanisic and Leon Goretzka, who trained with the ball again on Thursday for the first time after a knee problem.
Sunday’s opponents Hertha are four points from the bottom three after a series of inconsistent results.
Coach Tayfun Korkut wants a reaction after losing the Berlin derby 3-2 at home to Union on Wednesday in the German Cup, but admitted “you can’t make up for a derby defeat with the next game — even against Bayern”.