Bayern have been irresistible in their last two games, scoring seven in each, and suddenly appear to have gained momentum at the right time in the season after a slump which including defeats to Borussia Monchengladbach and Bayer Leverkusen.
If anyone can stop find a way of stopping them, however, it is the 73-year-old Rehhagel, who led Kaiserslautern to an improbable Bundesliga title in 1998, the only time a promoted team has won the championship, and won Euro 2004 with Greece, an equally unlikely achievement.
Rehhagel's total of 18 wins over Bayern at various stages during his career is more than any other coach has managed and "King Otto" is always happy to put one over on the Bavarian club who sacked him after less than a season back in 1996.
In complete contrast to Bayern, Hertha, who are 16th with 23 points and occupy the relegation playoff spot, have found goals almost impossible to come by, scoring only once in their last seven outings in all competitions.
"We create plenty of chances but we can't put the ball in the net," said Rehhagel, who has managed one win and two defeats since becoming Hertha's third coach of the season.
Bayern, second with 51 points, are still five behind leaders and titleholders Borussia Dortmund, with nine games each to play, including a meeting between the two sides on April 11.
Jurgen Klopp's team host sixth-placed Werder Bremen and are attempting to set a club record of 20 Bundesliga matches without defeat, their last reverse having come against Hannover 96 in September.
They had also won eight games in a row until being held to a goalless draw at Augsburg last week.
Borussia Monchengladbach have dropped back into third spot, three points behind Bayern, after picking up only one point and failing to score in their last two games and hope that a visit to local rivals Bayer Leverkusen will inspire them to an improvement.
"Maybe Leverkusen's attacking goal will favour us," said striker Marco Reus, whose side won the corresponding fixture last season 6-3.
"We simply have to work harder in training and we will start winning again."
The weekend also features a key relegation battle with Hamburg SV, who have dropped into 14 place with 27 points, facing 17th place Freiburg, who have 22.
Hoffenheim, Bayern's victims last Saturday when they lost 7-1, hope for an easier time when they host VfB Stuttgart on Friday evening.
Coach Markus Babbel admitted he got some grim satisfaction out of seeing Bayern beat FC Basel 7-0 in the Champions League on Tuesday.
"Maybe we're not the only village idiots, it's happened to someone else" he said. "That was a confirmation of how strong Bayern are."
