The Advocate General of the European Court of Justice will on Thursday publish a long-awaited opinion on a contested 2.4-billion-euro ($2.6-billion) fine that Brussels slapped on Google for anti-competitive practices.
Although such opinions are not binding, they do carry weight and are often followed by EU judges in their rulings.
In this case, the opinion will feed into a legal battle Google has been waging to overturn the fine the European Commission hit it with in 2017.
The commission determined that Google abused its dominant position by favouring its own Google Shopping service in results from its ubiquitous search engine.
Google, owned by US tech titan Alphabet, was forced to change how it displays search results.
At the time the fine was a record. But it was overtaken in 2018 by a 4.3-billion-euro penalty Brussels levied on Google for putting restrictions on Android smartphones to boost its internet search business.
Google lost a first round in its challenge over the Google Shopping case when the lower EU General Court in 2021 upheld the commission's conclusions and penalty.
Google then mounted an appeal to the higher EU Court of Justice with an argument that Brussels was going too far and misunderstanding how corporate competition works.
The Advocate General, Juliane Kokott, is to deliver her opinion at 0830 GMT.
The Luxembourg-based court, though, is not expected to hand down a ruling in the case for several more months. It could decide to confirm or overturn part or all of the lower court's decision.
The European Commission has hit several US Big Tech companies with fines in recent years as it seeks to regulate online services and better protect European consumers and firms.
Last year the EU brought in laws, the Digital Services Act and the Digital Markets Act, that crack down on illegal online content and impose tough new curbs on internet giants.
Google has so far borne the brunt of the European Commission's antitrust scrutiny, racking up a total of eight billion euros in fines.
It is currently the target of another probe by Brussels, launched in 2021, to see whether it abused its position to favour its online display advertising technology, including on YouTube.
Depending on the outcome, that could result in another massive fine and a requirement that Google change its practices.
Alphabet in the third quarter of last year brought in $76.7 billion in revenue, most of it from online advertising, making $19.7 billion in profit.
In 2022, the tech giant had annual revenue of $282.8 billion.