What happened

Shares of restaurant delivery specialist Grubhub (NYSE:GRUB) were getting sent back to the kitchen last month as they fell 15%, according to data from S&P Global Market Intelligence.

After Grubhub saw profits wither in its February earnings report due to increased spending to fend off competition, the stock again got rocked in March as analysts pointed to the threat from fast-growing start-up DoorDash.

A man ordering with Grubhub through an app.

Image source: Grubhub.

As you can see from the chart below, the stock's worst day of the month came on March 19 when KeyBanc analysts issued a concerning report on Grubhub.

GRUB Chart

GRUB data by YCharts.

So what

Grubhub shares slipped 8.4% on March 19 as KeyBanc Capital Markets pointed to the threat from DoorDash, the start-up now valued at $7.1 billion. The analysts said that Grubhub was struggling to retain customers in an intensely competitive market. They said, "diner retention, initial diner spend and peak diner spend all appear to be deteriorating," according to CNBC.

This isn't the first time evidence has pointed to Grubhub losing market share. Second Measure, a data analysis firm, found that Uber Eats was taking share from Grubhub last year, while DoorDash has more recently surged in the hot food-delivery market. Though Grubhub is still the market leader, its share has fallen from more than 50% to less than 40% over the last year.

KeyBanc said Grubhub's diner retention fell from 59% in the first quarter to 36% in the third quarter, and competition is only likely to increase, with DoorDash fresh off a new funding round and Uber and Postmates preparing for their IPOs.

Now what

The figures above should only build on worries about Grubhub's ability to grow profits this year and beyond, as analysts already see earnings per share this year falling from $1.66 to $1.41. Grubhub itself forecasted a modest increase in its adjusted EBITDA for the year.

Considering that its rivals are about to become more capitalized and that Grubhub, despite its many restaurant partnerships and acquisition strategy, has no true competitive advantage, the stock could be in trouble. Grubhub will have to find a way to stem the market share losses, or the stock could have further to fall.