In a statement, Olympus confirmed that it faces a 6.6 billion yen lawsuit from Japanese medical equipment provider Terumo - a firm that hopes to merge with Olympus in a £400m deal that could scupper Sony and Fujifilm's bids to form an alliance.
Olympus's share price fell more than 70% in the weeks immediately following exposure of accounting irregularities at the end of last year, before recovering to around half its former value at the start of 2012.
Terumo is also seeking interest at 5% a year dating from August 2005 when it was allocated nearly 7m shares worth more than £120m, according to a statement issued by Olympus Tokyo.
Terumo, which owns 2.1% of Olympus, is seeking damages under Japanese laws that require a firm to declare its true financial position to regulators through a securities registration statement.
Olympus is confident that similar lawsuits from other institutional investors will not follow, saying that Terumo was the only company that acquired shares 'in the primary market during the period for which the lawsuit can be filed'.
Meanwhile, Terumo claims that the legal action will not affect its proposed ‘integration' with Olympus ‘in any way.'