Carrefour SA (CRRFY)  can't seem to win. Europe's biggest supermarket operator and the second biggest retailer in the world behind Walmart (WMT) - Get Report on Friday, July 7, posted an unexpected uptick in second quarter sales but saw its shares tank all the same.

Carrefour stock fell almost 5% to €21.33 ($24.35) in early trading, making it the worst performer on France's key CAC 40 index, as investors disregarded the top line growth and chose to fret over the group's under pressure profit margins.

Not that anyone knows what they are. Carrefour's CFO Pierre-Jean Sivignon late on Thursday declined to tell analysts on a call whether earnings would match consensus expectations of €2.49 billion for 2017. That information will have to wait until August 30, when the company releases its first half-earnings, he said.

That no comment was enough to overshadow a 2.8% increase in second quarter sales on a like-for-like basis, which pushed revenues to €21.76 ahead of expectations of about €21.5 billion. The fear is that the sales increase has come at the expense of margin, particularly in Carrefour's key home market of France, where hypermarket sales reversed recent declines to climbed 0.5% after a 1.6% decline in the first quarter.

Sivignon did little to bolster confidence by telling analysts that the increase in France had come against a difficult backdrop and reflected price cutting.

In the absence of hard information analysts were left to speculate on how deeply margins had been cut. Deutsche Bank shaved its earnings per share forecast by 5% for 2017 by 3% for 2018. Goldman Sachs said the lack of information likely confirmed its pessimistic EBIT prediction of about €2.44 billion.

Carrefour's ongoing home front woes have also overshadowed plans, announced last month, to float its Brazilian operation in an IPO that could value the unit at as much as 37.6 billion reais ($11.5 billion). Because of that pending IPO Carrefour is banned from releasing sales figures for the Brazilian unit.

The company is also preparing to change its CEO. Alexandre Bompard will replace the current head Georges Plassat on July 18. If analysts' earnings fears are confirmed the new man will have his work cut out for him.