PARIS (Reuters) - Shares in French retailer Casino CASP.PA sank as much as 15 percent on Friday amid fresh concerns over its debt burden.

FILE PHOTO: A logo of French retailer Casino is pictured outside a Casino supermarket in Nantes, France, July 20, 2017. REUTERS/Stephane Mahe//File Photo

This came as U.S. short seller Muddy Waters said on Twitter that one of Casino’s subsidiary had not filed its 2017 accounts.

The Muddy Waters tweet carried a link to public records company Infogreffe, which showed the Casino Finance unit did not file its 2017 accounts.

A Casino spokesman however said the delay was merely “technical” and that the accounts of the Casino unit were already integrated into Casino 2017 consolidated accounts.

“The accounts will be filed tomorrow and available on Infogreffe next week,” he said

Casino shares narrowed their losses to 9 percent after the comments.

Casino stock has lost 45 percent so far this year partly on concern over the level of its debt and that of parent company Rallye GENC.PA, whose shares are down 39 percent.

Casino, which had its credit rating cut to junk by Standard & Poor’s in March 2016, said in June it aimed to complete 1.5 billion euros of asset sales by early 2019 to reduce its heavy debt burden.

In 2015 Muddy Waters criticized Casino’s accounting practices, saying the supermarket retailer was “dangerously leveraged” and managed for the short-term.

Muddy Waters said at the time that it was “short” on Casino’s shares and credit, namely betting on falls in both assets.

Casino had rejected Muddy Waters’ criticism at the time.