Advocate General Juliane Kokott proposed on Thursday that the European Court of Justice should set aside a 2007 ruling by the Court of First Instance which annulled a European Commission decision taken in February 2006.
The European Union executive had appealed against that ruling.
"There is therefore no infringement of the general principle of equal treatment and non-discrimination," Kokott said in a written opinion on the case, which the Court is not obliged to follow.
"Contrary to the assertion made by Alrosa, the decision at issue was not arbitrary either, but was based on objective considerations, in particular the results of a market test conducted by the Commission," she said.
Kokott said the ECJ should dismiss Alrosa's appeal to the lower court for an annulment of the Commission decision, and order the company to pay court costs.
World No. 1 diamond producer De Beers settled a monopoly abuse case with the European Commission by agreeing not to buy rough diamonds from Russian diamond miner Alrosa from 2009.
The Commission said this would make more diamonds available in the market.
Alrosa, the main rival to De Beers, produces one quarter of the world's rough diamonds. De Beers is 45-percent owned by mining group Anglo American Plc.