Google could face a record fine for failing to comply with EU competition rules, the European Commission has said.
The warning comes after four years investigating the search engine giant, with Google now ordered to put forward proposals to remedy the issue in order to avoid the fine.
The firm currently faces 20 complaints from its rivals - including Microsoft, which previously faced an EU investigation lasting 16 years.
Joaquin Almunia, the European Commission's competition chief, told MEPs that the complaints had provided fresh evidence against some of the proposals put forward by Google.
"We now need to see if Google can address these issues and allay our concerns," he said.
The investigation was initially launched back in November 2010 following claims that Google was using its 95 per cent market share in Europe to distort search results, making sure its products and services compared favourably against its competitors.
The investigation has also looked into the way Google displays content from other websites without permission.
It did appear that the European Commission was set to accept Google's offer of remedies, the third proposal put forward by the firm, but this is no longer the case following lobbying by the German and French governments.
Ideally, Almunia would prefer to reach an agreement with Google, as a decision to fine the company would probably be accompanied by years of "uncertainties and would not necessarily be good for consumers."
The final decision on the investigation is likely to be left to Almunia's successor, with the commissioner set to leave the EU executive next month.
The ruling could see Google fined up to 10 per cent of its 40 billion euro (£31 billion) annual turnover - €4bn.
The largest competition fine ever received was by Microsoft, and totalled 2.2 billion euros (£1.7 billion)