The lawsuit filed earlier this year says Google requires Android handset manufacturers such as Samsung Electronics to restrict competing apps like Microsoft's Bing search, partly by making Google's own apps the default.

The consumers claim these deals raise smartphone prices, because Google's rivals are not allowed to compete for premium placement on phone screens.

At a hearing on Thursday in a San Jose, California, federal court, US District Judge Beth Labson Freeman questioned whether that theory is too vague for the lawsuit to proceed.

"The speculative nature of the damages is really quite concerning to me," Freeman said.

The judge said she would most likely dismiss the lawsuit, but give the plaintiffs an opportunity to revise it with additional facts to try to proceed on some legal claims.

Last month, the European Parliament overwhelmingly passed a non-binding resolution urging antitrust authorities to break up Google. The lawmakers called on the European Commission to consider proposals to unbundle search engines from other commercial services.

Google argues in its court filings that the proposed class action should be dismissed because consumers still are free to use the other apps. The plaintiffs counter that most consumers either do not know how to switch default settings, or will not go to the trouble.

Should Freeman ultimately allow the proposed class action to proceed, plaintiffs' attorneys would be allowed to delve into internal Google emails and contracts with smartphone companies, and could interview Google executives under oath.

In court on Thursday, Google attorney John Schmidtlein said the case should be dismissed because plaintiffs had not produced any evidence that handset makers actually wanted to use a different search engine.

In response, plaintiff attorney Robert Lopez countered said consumers should be allowed to examine Google's documents to learn those details.

But Freeman said US law mandates that plaintiffs present enough facts in their lawsuit "before I open the floodgates" to expensive discovery.