United lifted its unit revenue guidance and posted good results for December, Cramer said. Revenue passenger miles increased 2.6% for the month.
So is that good news or bad news for Delta? Well, Cramer reasoned that United's good results are driving the expectations higher for Delta, which makes for a less-ideal situation.
That being said, perhaps Delta also had a good month, Cramer said. Delta hasn't typically been a promotional airline and its management isn't privy to "pounding their chest" about how well it is doing, he added.
Partly because the company remains cautious, so, too, is Cramer until he hears otherwise from Delta and its management. He did note that the industry trades at a low valuation.
Shares of Delta are up 3.5% in 2017 and about 9% over the past 12 months. Analysts expect the company to earn 82 cents per share on $9.37 billion in sales.