What: Shares of GrubHub Inc (NYSE:GRUB) were down 10% as of 11:30 a.m. Monday following a downgrade from analysts at Cowen.

So what: GrubHub is set to release second-quarter results tomorrow morning, but Cowen analyst Kevin Kopelman stepped out today to downgrade the stock from "outperform" to "market perform." Kopelman also reduced his per-share price target on GrubHub from $39 to $30 -- an 11.2% discount from the previous close.

Specifically, Kopelman described "surprising" competition in GrubHub's online food ordering niche, and cited a proprietary delivery survey indicating several of GrubHub's competitors already offer a "differentiated and superior user experience." Most recently, those competitors include Yelp, which last quarter notably recognized around $5 million in revenue from its recent acquisition of GrubHub competitor Eat24. Kopelman also worries GrubHub's status as an early leader in the space is at risk of "eroding in the face of new delivery models."  

Now what: To be fair, last week Brean Capital analyst Tom Forte argued GrubHub's recent pullback represents a "buying opportunity" ahead of tomorrow's report, and reiterated his "buy" rating while assigning a $50-per-share price target. And though Forte acknowledged GrubHub is facing investor concerns over competition, he expressed optimism that GrubHub can still achieve its long-term goals.

Personally, however, I'd rather not trade around earnings volatility, and prefer instead to wait for more clarity from GrubHub management on the state of their business during tomorrow's call. Regardless of which way it swings, I think patient, long-term investors would be wise to hold their bets until then.