The FTSE 100 group said revenues were declining more sharply than expected, thanks to problems stemming from its £6.6bn acquisition last year of the software arm of Hewlett Packard.
Micro Focus said chief executive Chris Hsu had quit, just six months after taking the role, and would be replaced by chief operating officer Stephen Murdoch.
Executive chairman Kevin Loosemore said: “We remain confident in Micro Focus’ strategy whilst recognising that operational issues have led to a disappointing short term performance and outlook.”
Micro Focus, which manages older software for customers including banks and airlines, said revenues for the current financial year were expected to be 6%-9% lower, worse than the previously forecast 2%-4% decline.
It blamed “one-off” effects from the Hewlett Packard deal but said that the “fundamental thesis” of the acquisition was still sound.
The deal had catapulted Micro Focus into the ranks of Europe’s leading software makers.
But Monday’s warning saw shares slump 55%, leaving them at barely a third of their value at the start of 2018.
The stock had already been hit by a previous gloomy revenue outlook earlier this year.
Russ Mould, investment director at AJ Bell, said: “The cracks in Micro Focus were clearly visible at its half-year results in January and today’s warning confirms the problems have got worse.
“Large acquisitions are inherently risky as they come with integration challenges.
“Micro Focus appears to have underestimated these challenges and is now suffering.”