Second-placed Leverkusen are all but assured of automatic qualification alongside league leaders Borussia Dortmund, five points in front, and a win against Bayern on Sunday would keep them in the title hunt with five games left.
For Bayern, in fourth place and desperate for a top three finish to have a chance at Champions League action next season under Heynckes with the final in Munich, defeat would be a huge blow.
One point behind sparkling Hanover 96, the distance to that elusive third spot could grow to four with defeat at home against Leverkusen.
"I have said that all my thoughts right now are with Leverkusen," Heynckes, who has twice coached Bayern before, told reporters. "I have a job to do and until the season is over I am not thinking about Bayern. "This game will be the key for our whole season and this is how we approach it."
"We have to win because a win keeps all our options open."
Heynckes, at 65 the oldest coach in the Bundesliga, knows exactly what it means for Leverkusen, perennial runners-up but never champions, to stay in the title hunt so late in the season.
They have choked at the final stretch so often they have been nicknamed "Neverkusen", for faltering just before the finish line.
The good news for Heynckes is that attacking midfielder Renato Augusto and goalkeeper Rene Adler are back fit and should play in Munich.
Germany captain Michael Ballack, who has won back his starting spot after a long injury absence, is also relishing a return to Bayern, the club he played for before joining Chelsea.
"Bayern have just missed out on automatic Champions League qualification and that is deadly for them. The whole club is under enormous pressure and if we win we can really hurt them," said the 34-year-old.
The reigning champions took drastic measures to keep their hopes for a spot that leads at least to the Champions League qualifying rounds alive, sacking coach Louis van Gaal last week after a dismal 1-1 draw at Nuremberg.
His former assistant Andries Jonker took over for the remainder of the season.
While club bosses hope the change will be a wake-up call for their players, Bayern will need to beat Leverkusen without key winger Arjen Robben and defender Holger Badstuber who are both suspended.
Borussia Dortmund, edging closer to their first Bundesliga title since 2002, need to beat in-form Freiburg on Sunday to keep Leverkusen at a distance.
At the other end of the table Felix Magath's 2009 champions VfL Wolfsburg have their backs to the wall, needing a victory against struggling St Pauli to get out of the bottom three.
Borussia Moenchengladbach, in last place, travel to Mainz 05, hoping last week's big win over Cologne will give them the necessary confidence boost to battle against the drop.
