The embattled Swiss financier, Martin Ebner, is leaving the board of the struggling engineering group ABB with immediate effect.
A statement from ABB headquarters in Zurich said Ebner had stepped down for "personal reasons".
Ebner, who joined the ABB board in 1999, is the largest single shareholder in the company, owning a nearly ten per cent stake through his BZ Group.
The group refused to comment on what Ebner might do with his shares in ABB, saying only that he was stepping down so he could devote his energies to BZ.
But a rally in ABB's share price following news of his departure led to speculation that part of his holding might have already been sold.
Analysts said the markets had discounted the possibility that Ebner might flood the market with his stock.
That view was bolstered by Monday's announcement by US fund manager, Putnam Investment Management, that it had increased its stake in ABB to five per cent. Trader speculated that some of those shares might have come from Ebner.
BZ spokesman Kurt Schiltknecht said his departure "has nothing to do with the stake [in ABB] or anything else. "He would like to concentrate his efforts on our group."
Earlier this month, the BZ Group put its nearly 20 per cent stake in the Lonza specialty chemicals company up for sale.
The move fuelled speculation that it might also sell off stakes in other major Swiss companies, including the Credit Suisse Group and the Bâloise insurance company.
Under increasing pressure from the depressed stock market situation, BZ in July was forced to sell its controlling stakes in four listed investment funds to the cantonal bank of Zurich.
CS and other banks agreed then to give BZ a year's grace on an estimated SFr3 billion in due loans. On Friday, BZ reported that the banks remained committed to the agreement.
swissinfo with agencies