What happened Shares of Azul (NYSE: AZUL) were down more than 5% on Monday after the Brazilian airline was hit with a downgrade by J.P. Morgan. Airlines have rallied so far in 2021, and at least one analyst is worried they've gone up much too quickly. So what By Latin American airline standards, Azul has weathered the pandemic relatively well. The stock fell nearly 90% in the early days of the outbreak and is still off by about 50% since the beginning of 2020, but Azul was able to remain flying even as some of the largest airlines in the region fell into bankruptcy. Image source: Getty Images. Heading into trading Monday, Azul shares were up nearly 15% in the last few weeks after winning some positive analyst commentary. But the stock took a U-turn today after J.P. Morgan's Fernando Abdalla downgraded it to underweight from neutral. The airline rally, according to Abdalla, has outpaced the change in business fundamentals. The analyst is worried corporate demand will likely take significantly longer to recover than bulls hope, and he says there is more downside risk than upside potential in the shares right now. Now what Abdalla isn't worried Azul can't survive. Rather, he thinks a recovery will take much longer than investors hope. I have similar fears about U.S. airlines, and question whether the current bout of optimism is sustainable. For long-term holders, Azul is one of the best operators among South American carriers and should have a bright future. But this is not a good time for speculation about a so-called "reopen rally," as there is likely more turbulence for the airlines up ahead. As Abdalla warns, now is a good time for caution on shares of Azul and other airlines. 10 stocks we like better than Azul S.A. American Depositary SharesWhen investing geniuses David and Tom Gardner have a stock tip, it can pay to listen. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has tripled the market.* David and Tom just revealed what they believe are the ten best stocks for investors to buy right now... and Azul S.A. American Depositary Shares wasn't one of them! That's right -- they think these 10 stocks are even better buys. See the 10 stocks *Stock Advisor returns as of February 24, 2021 Lou Whiteman has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.Source