The proposed IBM-Sun deal is still on, but discussions could take several more days as IBM lawyers perform due diligence, according to Reuters.
The news service cited "people with knowledge of the matter" as saying that a deal is unlikely to be struck before next week at the earliest, as IBM looks at various parts of Sun's software and server business.
But the move could raise anti-trust concerns with US regulators, the report said. Sun and IBM have a combined 65 per cent of the $17bn (£11.7bn) market for Unix servers, which are mainly used by large enterprises and government organisations.
IBM still leads the server space with nearly a third of the market, followed by HP, Dell and Sun.
Sun has been seen by analysts as vulnerable to an acquisition for some time, given that it has never been fully able to monetise its technology assets and recover from the drop in demand for its high-end servers at the beginning of the decade.
Reports in The Wall Street Journal suggest that IBM may offer nearly double Sun's Tuesday closing share price of $4.97 (£3.58), in a cash deal totalling around $6.5bn (£4.68bn). The newspaper said that IBM is examining the terms of Sun's various technology licences to check for any conflict with IBM's business.
Sun's shares closed on Friday down 6.14 per cent at $8.10 (£5.60) on the Nasdaq, giving the company a value of about $6bn (£4.1bn).