The sudden departure sent the shares tumbling 142.5p to pounds 17.82. A source close to Micro Focus said Mr Gumucio's exit reflected the company's disappointingly slow move into information technology services and products.
Mr Gumucio was unavailable for comment last night.
Although Micro Focus "took a step in the right direction" with the purchase of Millennium UK, a year 2000 consulting company, the source said the company's hesitant progress in the IT services sector had been "frustrating".
However, he added: "Marcelo joined Micro Focus at a point when it was losing a great deal of money. The revenues are now on the increase and costs are under control." In the past 15 months the share price has more than doubled.
Micro Focus said he would be replaced by Martin Waters, the former chief executive officer of Platinum Solutions who had been working as a consultant at Micro Focus. Mr Waters, who has 20 years' management experience in IT groups, will be president and chief executive officer.
The management changes will come as a blow to the company, which had only just begun to recover from a difficult few years. Although Micro Focus shares, which are among the most volatile on the market, are still well below their 1993 high of pounds 30, the stock has recently soared from its all-time low of 588p.
The company said the terms of Mr Gumucio's resignation were still being resolved. However, he was only three months into a year-long contract.
Mr Gumucio earned pounds 231,000 in the year to the end of January, of which pounds 129,000 was paid in performance-related bonuses. He is to resign the 660,500 options he continues to hold in the company.
Mr Gumucio joined in January last year from Memorex-Telex. He arrived at the company less than two weeks after it reported a full-year pounds 6.5m pre-tax loss. Micro Focus said he would continue to work as a consultant and he had returned to his family-owned investment firm, Gumucio, Burke & Associates.