Leverkusen, in second place nine points off leaders Borussia Dortmund, would close to six points if Dortmund stumble against Mainz 05 on Saturday but defeat could leave them 12 points adrift and make a title challenge all but impossible.
The clash against Champions League quarter-finalists Schalke has been overshadowed by the coaching sagas at both clubs.
Schalke sacked Felix Magath on Wednesday while Heynckes, who has not yet signed a contract extension, is being linked with a move south to Munich to succeed Louis van Gaal at champions Bayern.
Heynckes, who has twice before coached Bayern and is a close personal friend of club president Uli Hoeness, has not dismissed the reports, saying a decision on whether he will stay on at Leverkusen would fall early next week.
"On Monday or Tuesday we will sit down and announce a decision on this. I am very relaxed about it," Heynckes said before his team's Europa League match against Villarreal on Thursday.
With reporters wanting to know whether this would be his last European game at Leverkusen, the 65-year-old hinted he could be on his way out at the end of the season.
"Not if we win by two goals (to advance)," he said with his side having lost the first leg 3-2.
Leverkusen's good run this season has largely gone unnoticed, with Dortmund's spectacular season and Bayern's collapse in all competitions grabbing the headlines.
Heynckes' players want to keep it that way. "The team has shown it can deal with all this noise," Heynckes said.
Schalke have advanced to the Champions League last eight and are also in the German Cup Final but are out of contention in the Bundesliga, down in 10th spot.
"We all have to pull together now," said Schalke defender Benedikt Hoewedes. "After the club's decision it is important to keep a cool head now."
Leaders Borussia Dortmund share none of their worries when they host Mainz, in fifth place on 43, with their eyes firmly set on their first Bundesliga title since 2002.
Fourth-placed Bayern, following their last-gasp Champions League exit to Inter Milan in midweek, travel to Freiburg in a bid to edge closer to Leverkusen and challenge for second place and automatic Champions League qualification for next season.
They are seven points behind second spot.
