Add the prospect of being dumped from Japan's best-stocks index to Toshiba Corp.'s woes.

The Tokyo-based manufacturer, mired in an accounting probe, is racing against the June 30 deadline when members of the JPX-Nikkei Index 400 will be reassessed. Toshiba risks losing its place on the government-backed measure if it fails to file earnings by then, said Shinkin Asset Management Co.

Removal from the stock index, which is meant to identify Japan's most appealing companies for investors, would be another blow for Toshiba as it works to quantify the cost of its bookkeeping improprieties. It's also a headache for the JPX-Nikkei 400's creator, Daisuke Tanaka.