New Bayern Munich coach Thomas Tuchel said he had regrets over how his time with Borussia Dortmund came to an end but is now fully focused on his new role as they welcome his former team in a clash that could define the Bundesliga title race.

Tuchel returned to Germany to take over Bayern during the international break when they made the shock decision to sack Julian Nagelsmann with the team second in the Bundesliga and in the quarterfinals of the Champions League.

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The former Chelsea and Paris Saint-Germain boss previously coached Dortmund from 2015 to 2017, winning the German Cup in his second season.

But he chose not to dwell on the past as he prepares to lead his new side against his former employers, who are a point ahead in the league.

"I think it's better if we leave it alone. It makes little sense to publicly stir up the dregs. The mood is very forgiving and everyone sees it that way," Tuchel told a news conference before Saturday's game.

"When I played with PSG in Dortmund, I got hugs from a lot of people and hugged a lot of people too.

"There were also many regrets that things came to an end, but it's been too long to open that drawer. It doesn't do anyone justice."

Tuchel said his mantra at Bayern in his first week was "work, eat, sleep, repeat" even though some of his players only just returned from international duty.

"Training wise it feels like we've had a day. With meetings, scouting opponents, talking -- it felt like a month's work," he added.

"I was pretty tired in the evening but you want to soak up as much as possible. It's very demanding but at the same time, the best there is. I'm very grateful to be given the confidence at such a level."

Tuchel said Jamal Musiala had trained after he was ruled out of Germany's games due to a hamstring strain.

The winger, who has 15 goals and 12 assists in all competitions this season, will have another session on Saturday before they make a decision on his return.

However, Mathys Tel, Lucas Hernandez and Manuel Neuer are out for Der Klassiker.

Meanwhile, Dortmund manager Edin Terzic said his side "show a different face" if they are to end their long-running winless streak at rivals Bayern.

"What makes me particularly confident is the energy we have developed. This is because of our run, for example, and many good results," Terzic told reporters.

"We know our chance, and we want to take it. We have to do everything we can for that. We set out with the goal that we have to invest everything. We can send a signal -- both to ourselves and to the competition.

"Tomorrow's game can set a direction, but it won't decide everything... We must courageously seize our opportunities and show a different face tomorrow than we have in recent years in Munich."

He added that Dortmund will be without Giovanni Reyna and Thomas Meunier for Saturday's game, while Jamie Bynoe-Gittens and Nico Schlotterbeck's participation is in doubt due to injuries.