"Google appears to be strategically deploying universal search in a way that degrades the product so as to slow and exclude challengers to its dominant search paradigm," the researchers said.
It's not all bad, though: There are some instances, such as displaying time or presenting a calculator, where Google favoring its own services does not harm consumers, they found, adding that presenting a calculator on top of a search result page is preferred by users.
Google did not immediately respond to a request for comment. The company has always denied that it violates European antitrust rules.
The Commission opened its antitrust investigation into Google's search practices in 2010, triggered by complaints from competitors. Google was formally charged with abusing its dominant market position as a search provider in April. The Commission said Google violates European antitrust rules by systematically favoring its own comparison shopping product over competing services, a practice that hurts consumers and stifles competition.
A redacted version of the charges was sent to Google's foes earlier this month; they were given four weeks to respond. Meanwhile, Google has still to respond to the Commission's charges.
Sign up for CIO Asia eNewsletters.