Sistema has now lost almost half its market value since Rosneft filed its lawsuit against the firm in May.
As of 0800 GMT, Sistema’s Moscow-listed shares had pared their losses to trade down 8.4 percent on the day, while those of the MTS telecoms firm in which it owns a large stake were down 3.7 percent.
Equity analysts said the Sistema-Rosneft dispute would cast a pall over the broader Russian market.
“However the further fate of this case develops, such news erodes the hopes of market players for a favourable investment climate in future,” said Alexei Antonov at Alor Broker.
Russia’s rouble-based MICEX index was 0.1 percent lower at 1,858 points, while the dollar-denominated RTS index was also down 0.1 percent to 991 points.
According to a court order, a 31.76 percent stake in MTS owned by Sistema has been frozen, 100 percent of its Medsi chain of medical clinics, and 90.47 percent of the Bashkirian Power Grid company owned by Sistema and its unit Sistema-Invest.