Bayern Munich CEO Karl-Heinz Rummenigge has finally ended speculation that Jupp Heynckes could return next season, while also saying he is so confident that Robert Lewandowski will not be leaving this summer that he is "willing to take bets."

Bayern hired Heynckes as interim coach in October after Carlo Ancelotti's dismissal, and though he was widely expected to step down after this season, the 72-year-old earlier this month insisted he had never said he would definitely retire.

However, Rummenigge confirmed ahead of Bayern's Der Klassiker clash against Borussia Dortmund on Saturday that Bayern would be looking to hire a new coach before the end of April.

"It's Heynckes wish to retire at the end of the season," Rummenigge said.

But the CEO also said that Bayern will not pursue any coach who does not speak the local language.

"We want a German-speaking coach," Rummenigge added. "That's the way it will be."

Rummenigge also confirmed multiple reports this week that said former Dortmund boss Thomas Tuchel had rejected Bayern's offer to succeed Heynckes and had already pledged his services to another team.

"Our sporting director Hasan Salihamidzic has held talks with coaches and Tuchel was among them," the CEO said, noting that he couldn't say a "bad word" about Tuchel.

"He informed us that he's signed for another club. But that isn't a problem for us, we are relaxed."

Former Bayern legend Lothar Matthaus has strongly suggested that Eintracht Frankfurt's Niko Kovac, a former Bayern defender and coach of Croatia, is a leading contender for the job.

As for the upcoming transfer window, Lewandowski's split from his agent last month added fuel to reports that Real Madrid are interested in signing the 29-year-old, but Rummenigge told Sky that Bayern were not looking to sell the Poland international.

"I know they are well aware at Real Madrid that Robert Lewandowski has a three-year contract with us," he said. "He will definitely stay with us next season at Bayern. I'm willing to take bets on that."

Heynckes had also refuted the transfer rumours in his prematch news conference a day earlier, saying: "I know the Spanish media, there is a lot of speculation. I assume that Lewandowski will break my Bundesliga goal-scoring record in the next two or three years."

ESPN FC's Bayern Munich correspondent Mark Lovell contributed to this report.