The two prolific goalscorers are expected to come face-to-face on Wednesday (AEST) when Dortmund hosts Bayern at Signal Iduna Park in the 2021 DFL-Supercup, a trophy the Bundesliga champion has won in four of the last five campaigns.
Haaland enters the match on the back of a strong start to the season, having followed up a hat-trick against lower-league Wehen Wiesbaden in the DFB-Pokal with two goals and two assists in Sunday's (AEST) 5-2 Bundesliga victory against Eintracht Frankfurt.
Norway international Haaland now has 62 goals in 61 appearances since making his BVB debut in January 2020, including 42 goals in 44 Bundesliga games for an average of 1.06 goals per 90 minutes in the competition.
Only ex-Dortmund man Lewandowski can better that return over the same period, scoring 57 goals from an identical number of appearances in the German top flight – an average of 1.35 per 90 minutes.
While Nagelsmann has been impressed by Haaland's incredible season-and-a-half in the Bundesliga, the recently appointed Bayern boss still thinks the 21-year-old has some way to go to match Lewandowski's consistency.
"Lewandowski has proven over several years now that he is a world-class striker," Nagelsmann said at Monday's pre-match news conference. "Erling hasn't been in the league that long, though his scoring rate is great.
"The other difference is age. Lewandowski has a lot more experience on his side than Haaland. In terms of similarities, they are both an unbelievable goal danger. But I am incredibly happy to have Lewandowski here."
The weekend win over Frankfurt was the first time Haaland has provided two assists in a single competitive game for Dortmund in his 19 months at the club.
Keeping Haaland off the scoresheet on Tuesday will be a huge task, but Nagelsmann is confident his players – including goalkeeper Manuel Neuer – are capable of doing so in the battle between last term's German cup and league winners.
"He is of course an excellent striker. Extraordinary. In addition to his goals, he is also robust and fast," Nagelsmann said. "We have to get close to him to prevent him from making runs in behind our defence.
"We have to be physically ready and be prepared to initiate the counter-press after we lose the ball so that quick passes up the other end of the field are prevented. We can't prevent that completely, but we still have the best goalkeeper in the world."
Nagelsmann has endured a difficult start to life as Bayern boss, not helped by a number of players returning late to training, with the reigning Bundesliga champion yet to win any of his five games in charge.
Bayern was held 1-1 by Borussia Monchengladbach in their first competitive game under Nagelsmann on Saturday and the 34-year-old coach is eager to get off the mark with some silverware in midweek.
"I would like to sign for a win tomorrow and then go on and take the title," he said. "Dortmund have started the season well, whereas we're still waiting for that first win, but I wouldn't look into that too much.
"Of course this is an important match for us, but it's not necessarily important for the rest of the season. Both teams have a few injuries and the season is still young, but we are going there with the aim to win."
Nagelsmann also paid tribute to Bayern's all-time leading goalscorer Gerd Muller, who passed away at the weekend at the age of 75.
"My condolences to Gerd's family and friends," Nagelsmann said. "Yesterday was a sad day for everyone involved in the club. Gerd played a lot of great games and scored some great goals."