Businessman Christo Wiese stunned crisis-hit Steinhoff with a $5 billion lawsuit on Thursday, sending shares of the South African multinational retailer fighting for survival after it uncovered accounting irregularities down 17 percent.

The 59 billion rand ($5 billion) claim is the latest setback for the retailer in which Wiese was chairman and biggest shareholder until December last year. Steinhoff’s share price has tumbled more than 90 percent following the scandal, which also triggered a cash crunch.

Titan Group, which houses some of Wiese’s family assets, said the claim related to the 2016 capital injection by Wiese to help Steinhoff to pay its debt and fund the acquisition of the U.S. company Mattress Firm.

The claim also relates to the acquisition by Steinhoff of Wiese’s clothing retailer Pepkor in 2015, in which Wiese and other Pepkor shareholders subscribed for Steinhoff shares as part of his payment.

Steinhoff said in a statement it would assess Wiese’s claim and determine the appropriate course of action.

Wiese’s 22 percent shareholding in Steinhoff fell to around 6 percent after banks he had borrowed money from exercised the security rights over the stock because had used the stock as collateral.

Shares in Steinhoff fell as much as 17 percent on Thursday to 1.83 rand, valuing the company around 8 billion rand, a dramatic fall from grace for the stock that was valued at around 200 billion rand just four months ago.

Wiese, best known for transforming grocery retailer Shoprute from just six shops in the 1970s to hundreds of stores across Africa, said in a statement he was open to working with shareholders claiming damages against Steinhoff.

“Many of the other businesses in the Steinhoff group offer good prospects and I strongly believe every attempt possible should be made to restructure the group as expeditiously as possible,” Wiese said.

Steinhoff is already in talks with creditors about restructuring its debt, its acting chairperson Heather Sonn told investors last week at the company’s first meeting with shareholders since the scandal.

Separately, Steinhoff sold its 50 percent in German furniture chain POCO to former joint venture partner Andreas Seifert in a bid to settle a lawsuit over the ownership of the business.