What happened

Shares of Kroger (NYSE:KR) modestly underperformed a weak market last month, losing 12% compared with a 7% decline in the S&P 500, according to data provided by S&P Global Market Intelligence.

The decrease added to a tough year for shareholders, with the stock down 14% so far in 2019 versus a 12% increase in the broader market.

A man shops for groceries.

Image source: Getty Images.

So what

Kroger didn't announce earnings results last month. But its biggest competitors did, and those announcements point to continued pressure on the supermarket giant.

Walmart (NYSE:WMT), Kroger's No. 1 rival, posted its fourth consecutive quarter of over-3% sales growth. Management again credited market share growth in the grocery segment for helping power robust customer traffic. Likewise, Target (NYSE:TGT) said in late May it is winning share across all of its major product categories.

Now what

Normally, such positive comments by peers would lift expectations for Kroger's stock since the industry appears to be growing steadily. However, Walmart and Target have each picked away at the chain's market share in recent quarters, and the latest results imply that these trends continued into 2019. Moreover, both retailers are spending billions on rapid home delivery, which will add pressure on Kroger to do the same.

The company hasn't yet scheduled its first-quarter earnings release, but investors are hoping that the upcoming report can show an improvement over the 2% sales uptick Kroger managed in the prior full year.