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.

“We have no clear rule for when a company doesn’t have financial data,” said Tanaka, who works at Japan Exchange Group Inc., stressing he can’t comment on specific stocks. “We don’t usually envisage situations where a company doesn’t have data. We would have to decide on a case-by-case basis.”

Toshiba and one of its listed subsidiaries, Toshiba Plant Systems & Services Corp., are members of Tanaka’s index. The companies this month postponed earnings announcements amid an internal investigation into improper accounting on infrastructure projects, with Toshiba saying it will post results in June or later. It’s also revising profit figures for the previous three years.

The JPX-Nikkei 400, started last year, is intended to showcase the nation’s best shares to institutional investors and shame executives of companies that weren’t picked into improving capital efficiency to make the cut. It selects the 400 companies in Japan with the highest return on equity and profit over the past three years. Corporate governance is another factor in choosing the members.

The gauge recalculates its constituents every year using data from the last business day of June, and publishes the results in August. Sony Corp. was among 31 members that got replaced in 2014. Should Toshiba fail to report earnings in the next six weeks, or file restated figures for previous years, assessing its financial health becomes difficult.

“They could be removed,” said Naoki Fujiwara, Tokyo-based chief fund manager at Shinkin Asset, which oversees about $5.8 billion. “The stocks picked for the index have to meet fixed standards. If they don’t satisfy those criteria, you can’t compare equally and it becomes unfair.”

One area where the JPX-Nikkei 400 rules are clearer, and another concern for Toshiba, is when the bourse puts a stock on a watch list known as securities on alert. Companies on this list are ineligible for the share gauge, according to JPX. Olympus Corp. and IHI Corp., which admitted to accounting improprieties in the past, were both given this designation.

Toshiba estimated Wednesday that earnings in its last three fiscal years would be cut by about ¥50 billion. The investigation is ongoing and there’s little to suggest the reduction in profits will be limited to this figure, Goldman Sachs Group Inc. analyst Ikuo Matsuhashi wrote in a note published Thursday.

Naomi Furuya, a spokeswoman for Toshiba, declined to comment.

“We will announce our earnings as soon as we can,” said Masayuki Tamura, a spokesman for Toshiba Plant Systems & Services, declining to elaborate.

Depending on the severity of the transgressions that caused Toshiba’s revisions, it may be put on the watch list, Hideaki Hirose, a director at the bourse’s self-regulatory body Japan Exchange Regulation, said Wednesday before the company’s statement.

“They might be designated as a security on alert, or asked to submit an improvement report, or nothing might happen. We don’t know at this point,” Hirose said.

About ¥650 billion was tracking the JPX-Nikkei 400 in exchange-traded and mutual funds at the end of April, according to the exchange. Toshiba accounts for about 0.5 percent of the measure, data compiled by Bloomberg show. Its shares have slumped 12 percent this week through Thursday, wiping out about $1.9 billion in market value.

More problems may be awaiting Toshiba after its unit was among several companies called to testify to a congressional committee investigating Brazil’s largest corruption scandal. Luis Carlos Borba, president of Toshiba America do Sul Ltda., will be asked to explain contracts allegedly signed with a front company owned by convicted money launderer Alberto Youssef, according to a lower house statement Thursday.

“There’s no denying they might be kicked out” of the JPX-Nikkei 400, said Yoshihiro Ito, chief strategist at Okasan Online Securities Co. “If the bourse goes soft on this one, it’s going to impact the index’s importance.”