Google faced a setback after an advisor to the highest European court sided with EU antitrust bodies in their battle against a record fine of 4.34 billion euros ($4.98 billion) imposed on it seven years ago.
The European Commission stated in its 2018 decision that Google used its Android mobile operating system to hinder its competitors.
The lower court upheld the EU's decision in 2022 but reduced the fine to 4.1 billion euros, prompting Google to appeal to the highest European court.
Julian Kokot, the Advocate General at the European Court of Justice based in Luxembourg, advised the court in her non-binding opinion to reject Google's appeal and uphold the reduced fine imposed by the lower court, stating: "The legal arguments presented by Google are ineffective."
Kokot rejected Google's argument that regulators should compare Google with a competitor when assessing the situation, saying: "It is not realistic, in this case, to compare Google's situation to that of a similarly efficient hypothetical competitor."
Google has captured a dominant position in many Android markets, thus benefiting from network effects that allowed it to ensure users use Google Search.
The judges, who usually issue four out of five non-binding opinions, will deliver their rulings in the coming months.
A spokesperson for Google said on Thursday: "Android has provided more choices for everyone and supports thousands of successful companies in Europe and around the world."
He added: "We are disappointed with the opinion that, if followed by the court, would deter investment in open platforms and harm Android users, its partners, and app developers."
Regulators pointed out that Google's illegal practices date back to 2011, where it required manufacturers to pre-install its Google Search and Chrome browser, in addition to the Google Play Store, on their Android devices, and paid them to pre-install only Google Search, while preventing them from using competing Android systems.
Google's Android system, which the company provides to device manufacturers for free, powers about 73 percent of smartphones worldwide, according to StatCounter statistics.
The world's most famous search engine has accumulated total fines of 8.25 billion euros linked to three investigations that have spanned more than a decade, while other investigations are still ongoing.