With 28 goals in 22 league games, Lewandowski is on his way to being crowned the Bundesliga’s top-scorer for the fourth season running.
The Poland international has banged in 16 goals in his last 13 league games.
“That man is crazy. Just crazy,” Haaland told Norwegian TV, admitting he is a fan of his Polish rival.
“When I score, I’m one goal closer to catching him up.
“And then he just scores another hat-trick like it’s an everyday thing.”
Gerd Mueller’s all-time record of 40 goals in a single Bundesliga season is under threat.
At the same stage of the 1971/72 season, Mueller had scored 25 goals; Lewandowski has 28.
Despite missing a month with injury, Haaland, 20, has managed 17 league goals this season, but admits there is “a lot” he can learn from Lewandowski.
Bayern have won the club’s last four clashes, including a 3-2 win at Dortmund last November, when both Haaland and Lewandowski both scored.
That followed a 3-2 victory for Bayern in the German Super Cup in September, yet Dortmund fancy their chances at Munich’s Allianz Arena.
“This season we have shown in both games that we have gotten closer in recent comparisons,” Dortmund caretaker coach Edin Terzic told Kicker.
Both teams are in form.
Dortmund have won their last four games while Bayern have scored nine goals in their last two wins.
Thomas Mueller, having recovered from Covid-19, set up one of Lewandowski’s two goals in a 5-1 thumping of Cologne last Saturday.
Haaland can bank on the silky passes of England winger Jadon Sancho and Dortmund captain Marco Reus, who is back to his best after injury.
Bayern are top of the Bundesliga and 13 points clear of Dortmund, but only two ahead of second-placed Leipzig.
Fifth-placed Dortmund want a win in Munich to bridge the three-point gap to the Champions League places.
Leipzig have a tricky tie on Saturday at Freiburg, where they last won nearly five years ago.
Leipzig are without defender Willi Orban who has a broken hand.
Julian Nagelsmann’s Leipzig came from two goals down to beat Moenchengladbach last Saturday and knocked Wolfsburg out of the German Cup on Wednesday.
Mid-table Moenchengladbach host Bayer Leverkusen, who have been furiously denying reports this is a last chance for coach Peter Bosz.
Having topped the table in December, Leverkusen have since slipped to sixth, outside the Champions League places, with two wins in eight league games.
Goalkeeper Lukas Hradecky is sidelined by an Achilles injury while midfielder Florian Wirtz is in quarantine after testing positive for Covid-19.
One to watch: Alexander Sorloth
The 25-year-old set up both goals in Wednesday’s 2-0 German Cup win over Wolfsburg having headed the last-gasp winner over Moenchengladbach last Saturday.
Head coach Julian Nagelsmann compared Sorloth to a ketchup bottle, which requires patience after the Norwegian had struggled this season since his 20 million euros ($24 million) transfer from Crystal Palace.
“You never know when the time will come and too much ketchup will end up on your plate,” said Nagelsmann who hopes Sorloth’s form “will continue” at Freiburg on Saturday.
43 – goals Haaland has scored in 45 games for Dortmund in all competitions. Lewandowski managed 11 goals in his first 45 matches for Dortmund, where he spent four years until joining Bayern in 2014.
5 – the goals Lewandowski scored in his first 20 Bundesliga games, while Haaland managed 18 goals in the same amount.
8 – the assists both Lewandowski and Haaland have in all competitions this season.
Fixtures (all times 1430GMT unless stated)
Schalke v Mainz (1930)
Borussia Moenchengladbach v Bayer Leverkusen, Hoffenheim v VfL Wolfsburg, Freiburg v RB Leipzig, Eintracht Frankfurt v VfB Stuttgart, Hertha Berlin v Augsburg, Bayern Munich v Borussia Dortmund (1730)
Cologne v Werder Bremen, Arminia Bielefeld v Union Berlin (1700)