FRANKFURT/DUESSELDORF (Reuters) - Thyssenkrupp TKAG.DE should come up with a candidate for the vacant post of chairman by no later than September, two investor sources said, concerned that a lengthy search might further delay restructuring efforts at the German conglomerate.

A logo of ThyssenKrupp AG is pictured outside the ThyssenKrupp headquarters in Essen, November 23, 2017. REUTERS/Thilo Schmuelgen

Thyssenkrupp has been without both a CEO and chairman since Heinrich Hiesinger and Ulrich Lehner resigned last month, throwing the elevators-to-submarines group into crisis at a time of mounting shareholder pressure over strategy.

The resignations of the two senior figures at the company reflect a power struggle among Thyssenkrupp’s management and shareholders, which include activist investors Cevian and Elliott.

“The search for a new CEO should not take longer than 2-3 months. Of course, a chairman should be found before that,” said one of the people, who was not authorized to speak publicly about listed stocks.

Thyssenkrupp declined to comment. A company spokesman confirmed that a structured process was underway to fill both positions.

But if the search drags on investors impatient for change might increase pressure on the company.

There are few experienced candidates that are both suitable and available for the chairperson job. Seasoned executives that would, in theory, fit the bill, such as Siemens SIEGn.DE CEO Joe Kaeser and Linde LING.DE Chairman Wolfgang Reitzle, are busy.

Airbus AIR.PA CEO Tom Enders, who will step down next year, was approached for the chairman's position but declined, sources familiar with the matter said. Airbus declined to comment.

Thyssenkrupp has for years faced calls to simplify its sprawling businesses to become less complex, but this has proved a difficult undertaking for a company with many competing stakeholders, including activist investors, powerful labor leaders and a charitable foundation.

“The new chairman ... faces a complex task and has no time to prove himself,” one of the investor sources said.

Former Siemens board member Siegfried Russwurm, who left the group last year and joined the shareholders committee of engineering group Voith [VOITH.UL] in March, has also been mentioned as a candidate for the chairman or CEO job.

Russwurm, 55, did not immediately respond to a Reuters request for comment when contacted through Voith.

Talks are now underway with another potential candidate for the chairman position, one of the sources said.

The search is being handled by the 5-member nomination committee of Thyssenkrupp’s supervisory board, which includes representatives of the group’s two largest shareholders: the Alfried Krupp von Bohlen und Halbach Stiftung and Cevian, which together own 39 percent of the company.

Thyssenkrupp shares reached a two-year low on Friday following a report that Lanxess LXSG.DE CEO Matthias Zachert would not be available to join.

Its shares have fallen 18 percent this year, compared with a 4.5 percent drop in Germany's blue-chip DAX .GDAXI index.