Sun has suffered long-running financial problems
Oracle has so far failed to produce evidence to ease concerns that its purchase of Sun Microsystems would be anti-competitive, the EU has said.
Competition Commissioner Neelie Kroes said she was "disappointed" by the lack of proposals to placate EU worries.
Business software firm Oracle has proposed a $7.4bn (£4.5bn) takeover of hardware and software maker Sun.
The EU is concerned the deal could breach competition rules, leading to higher prices and less choice.
Doubts persist within the European Commission about Oracle having control of Sun's MySQL database business.
On Wednesday, a spokesman for Ms Kroes said the commissioner had "expressed disappointment that Oracle had failed to produce, despite repeated requests, either hard evidence that there were no competition problems or, alternatively, proposals for a remedy to the competition problems identified by the Commission".
Eben Moglen, founding director of the Software Freedom Law Center, said the comments were "bad news for Oracle".
The US Department of Justice has already given its approval to the deal, agreed in April.
'No conflict of interest'
Earlier this week, Sun said it would cut 3,000 jobs over the next year while it awaited the verdict of the EU investigation into Oracle's takeover, which is due on 19 January.
They are the latest in a series of cuts to be made by the firm, which has suffered prolonged financial woes. Oracle said last month that Sun was losing $100m (£61m) every month.
Oracle maintains that there would be no conflict of interest and has promised not to sell off MySQL to get the deal approved.
It is looking to strengthen its position against IBM, which abandoned its own attempts to buy Sun earlier this year.