His first challenge is to beat relegation-threatened Borussia Moenchengladbach, Heynckes's former club, on Saturday.
The 63-year-old coached Moenchengladbach for about nine years after spending 12 years at the club as a striker.
"This is everything but a dream start," the coach told reporters before his first training on Tuesday. "But Borussia had sufficient opportunities to get out of that situation."
Bayern are in third place, three points behind leaders VfL Wolfsburg with their backs against the wall in the defence of their title after a disappointing season.
Hertha Berlin are a point ahead of Bayern on 55, with Hamburg SV and VfB Stuttgart level on 54 points.
Heynckes does not have a magic wand but he must somehow boost Bayern's confidence in a few days after they sank to a 1-0 home defeat against Schalke 04 last week.
Moenchengladbach, on the other hand, are desperate to take advantage of the turmoil at Bayern to stay in the top flight. They are second from bottom two points off the safety zone.
EAGER UNDERDOGS
"Fact is we have to win our games," Moenchengladbach vice president Rainer Bonhof said this week.
Bonhof, who played with Heynckes for most of the 1970s at Moenchengladbach, said the role of underdogs suited them.
"Maybe it is not that bad that we are now chasing the pack, as we did it so well once before, just after the winter break."
Even if Bayern win they will be hoping Hertha Berlin, who travel to Hamburg on Sunday, may slip up.
But Hamburg, with an inferior goal difference to Bayern, have their UEFA Cup semi-final against Werder Bremen to play on Thursday and could be left drained after a seemingly endless schedule of matches in the past few months.
Improving Hertha have won their last two games to climb back into contention for the title but will again be without suspended striker Andriy Voronin.
Leaders Wolfsburg, whose 10-match winning streak ended with a surprise defeat at lowly Energie Cottbus last week, host Hoffenheim, who have not won in 11 matches, on Saturday when Stuttgart visit third-from-bottom Arminia Bielfeld.
