Bayern face Basel in the Champions League on Wednesday night after a 0-0 draw with Freiburg at the weekend.
That result saw Bayern fall four points behind Borussia Dortmund at the top of the Bundesliga, increasing the importance of Wednesday's clash in Switzerland as they look to avoid a repeat of last year's trophyless season.
It also showed Heynckes that there is no such thing as an easy game.
"We will not be underestimating Basel, especially after last Saturday," he said.
"Basel have impressed me with the way they have put together a well-organised side with a good mixture of experienced players, some of whom have played in the Bundesliga, and talented young players who have a big career ahead of them."
One of those players is Xherdan Shaqiri, who has already agreed to join Bayern from Basel in the summer.
However, the Switzerland international says he has no point to prove.
"I think I have already impressed them enough," he said. "I am concentrating on playing for FC Basel."
Bayern could do with Shaqiri now as they are currently suffering without Bastian Schweinsteiger, who will also be absent on Wednesday night.
David Alaba should take his place again, but Austria's player of the year still lacks the same experience and aura of Bayern and Germany's vice-captain.
"Alaba has shown that we can cover for him to a certain extent, but Bastian is our brains," said Heynckes.
"Schweinsteiger plays a big role for us. When Schweini was 20, he was not as influential as he was when he was 25 either.
"We need to work as a collective and talk more on the field to get back to where we were, and to where we want to be."
Basel coach Heiko Vogel says he is paying no attention to Bayern's recent league results.
"Tomorrow is the Champions League, not the Bundesliga," he said. "We have got to concentrate on our own strengths and not what happened against Freiburg, Stuttgart or Kaiserslautern.
"They have no influence on this game. Tomorrow is Basel against Bayern.
"We are playing a top-quality side and we are going to have to play very well and have the right attitude, but so too must Bayern."
Vogel is without veteran midfielder Scott Chipperfield and Philipp Degen, who both have thigh strains.
