Questions remain over Lewandowski's future after he said he wants to leave Bayern and is refusing to sign a new contract.
Lewandowski suggested no new terms had been proposed on his contract, which is due to expire at the end of the season with the Bundesliga champion.
However, Bayern chief executive Oliver Kahn insisted on Saturday that a "concrete offer" was on the table, while sporting director Hasan Salihamidzic accused Zahavi of attempting to turn his client's head.
Zahavi hit back at Salihamidzic as he warned Bayern it would not be sensible to risk losing Lewandowski on a free transfer, nor to deny him the opportunity to join Xavi's Barca.
"For Lewandowski, Bayern is history," Zahavi said. "Robert has the chance to move to the club he has always dreamt of. Why is Bayern denying him this opportunity?
"Actually, I didn't want to speak in public because I have great respect for this historic club. However, I cannot fail to react to Hasan Salihamidzic's statements.
"Of course you can keep Robert for another year, to be fair he has a contract until 2023, but I wouldn't recommend that to you."
Lewandowski scored 50 goals in 46 matches for Bayern this season in all competitions, making him the top scorer in Europe's top five leagues.
Meanwhile, Borussia Dortmund's Erling Haaland has recorded 29 goals in 30 games in all competitions this term, and has agreed to join Manchester City for the next season after the Premier League champions activated his £51million (€60m) release clause.
However, Zahavi suggested Bayern made their intentions to sign Haaland before City's announcement, with Lewandowski aware of the plans to replace him with the Norway international.
"[He is a] very intelligent person, not just the best striker in the world. He knows exactly what is happening around him and what FC Bayern had planned," he added.
"So Robert knew all along that Bayern wanted to replace him with Haaland. Erling's father even confirmed it, telling him in a personal conversation some time ago: 'My son comes to FC Bayern for 50 percent.'
"The football world is big, but there are no secrets..."