Apple COO Tim Cook has done such a good job of running Apple during CEO Steve Jobs absence that investors are now fearing what would happen to the company should he leave.

Piper Jaffray Gene Munster told the Wall Street Journal: "At this point, losing Tim Cook would be a bigger deal to investors than if Steve Jobs stepped aside. Just that thought makes my stomach tighten up."

According to the Wall Street Journal report, other technology giants have tried to woo Cook in recent years: “Motorola tried to hire him last year while Dell wooed the executive two years ago,” claims the report.

Co-head of the CEO practice at recruiters Korn/Ferry International Stephen Mader said: "Now it's clear that Tim Cook can run any technology-based company. He's a more attractive CEO candidate both inside Apple and outside."

Since Cook took the helm from Jobs (who took six months sick leave) in mid January, Apple's stock has risen 60 per cent, compared with an 18 per cent increase in the Nasdaq Composite Index.

This is the second time Cook has taken over the day-to-day running of Apple. Last time was in 2004 when Jobs was recovering from surgery to remove a cancerous tumor from his pancreas.

Cook is also credited with pulling Apple out of near bankruptcy when he joined the company in 1998. Needham & Co analyst Charles Wolf said: "He turned a company that was on the brink of bankruptcy into one that is generating a huge amount of free cash."