"Max Chuard is far out of his depth in a CEO role and should be terminated with immediate effect," Petrus said in a letter to Temenos board members. "Andreas Andreades should resign from Temenos. His role as de facto decision-maker makes it hard for Temenos to attract and retain world-class management talent."
Temenos shares have been battered this year after the group ditched its full-year guidance and reported a steep fall in third-quarter profit.
In October the company saw 900 million Swiss francs ($915 million) wiped from its valuation after a profit warning frightened investors and analysts.
Temenos said then that decision-making by its banking customers had become more cautious while its costs were rising.
Petrus, which has a stake of less than 3% in Temenos, said it had already written to directors to air its concerns and demand immediate launching of a comprehensive strategic review.
Management had been "clueless" and had denied that fundamental problems existed, it said.
"With a share price decline of -53% this year and -72% between the peak in May 2019 and the day of the Q3 2022 earnings warning, this uninspired and delusional approach of hoping for 'something' later triggered our decision to write to you," Petrus wrote.
"Now is your last chance to bring the ship in order and on course."
Temenos has been approached for comment.
($1 = 0.9826 Swiss francs)
(Reporting by Noele Illien; Editing by John Revill)
