“Dortmund are in a phase and playing refreshing football going forward.
“We have to keep up and not let the gap grow.”
The goals could flow with Dortmund striker Paco Alcacer scoring seven goals in his first four league games on loan from Barcelona.
Likewise, Lewandowski has scored 12 goals in his 15 games against Dortmund, who he left on a free transfer in 2014.
Both teams are waiting on key players.
Dortmund goalkeeper Roman Buerki picked up a knock in Tuesday’s 2-0 defeat at Atletico Madrid in the Champions League.
Bayern winger Arjen Robben trained individually on Thursday as he recovers from a knee injury.
Bayern will head north determined to claim a third straight win at Dortmund after last November’s 3-1 away league win and penalty shoot-out victory in the pre-season German Super Cup in August 2017.
“We are four points behind and of course we want to be top — we will come back, you can all be sure of that,” warned Mueller.
Fixtures (all times 1430 GMT unless stated)
Hanover v Wolfsburg (1930)
Hoffenheim v Augsburg, Werder Bremen v Borussia Moechengladbach, Freiburg v Mainz, Fortuna Duesseldorf v Herta Berlin, Nuremberg v VfB Stuttgart, Borussia Dortmund v Bayern Munich (1730)
RB Leipzig v Bayer Leverkusen, Eintracht Frankfurt v Schalke 04 (1700)