Lewandowski's contract with the Bavarians will expire in the summer of 2023 and rumours linking him with a move to Barcelona have intensified in recent days.
The 33-year-old was once again on the score sheet on Tuesday as Bayern Munich exited the UEFA Champions League at the quarterfinal stage following a 1-1 draw with Villarreal at the Allianz Arena, having lost the first leg 1-0.
The reigning FIFA Men's best player has struck 47 times across all competitions this season, underlying his importance to the German champions.
Kahn says Bayern cannot afford to lose their goal machine and he will remain at the club next season.
"Apparently there is a competition out there to see who brings out the biggest nonsense story about Robert Lewandowski," Kahn told Amazon Prime Video.
"It is very important to mention that we have a contract that is valid for another season. If there's something to report, then we'll do it, too.
"We are not crazy and discussing a change from a player who scores between 30 and 40 goals every season."
Kahn added on Bayern's disappointing exit from the Champions League: "It's always disappointing when you concede a goal just before the end."
"We could have made it 2-0 before that.
"You can't blame the team. They put everything into it, tried everything in the second half.
"There are few less pleasant teams to play against [than Villarreal]. To crack this kind of defence, you need a lot of patience, you have to keep running. If there's one critique, it's that we didn't take advantage of one or two scoring opportunities and should have created one or two more chances.
"It just wasn't meant to be. The team threw everything in. We didn't lose the battle today [but in the first leg], more commitment and will is hardly possible.
"We're not going to cry, we're going to go for it again next year in the Champions League.
