(Reuters) A top executive of Russian gas monopoly Gazprom is expected to meet with EU antitrust chief Margrethe Vestager next month in a meeting that could determine the outcome of the EU's case against the company, a person familiar with the matter told Reuters Friday.

The Russian state-controlled company is fighting accusations of overcharging customers and blocking rivals in Eastern Europe, a case that could mean a hefty fine and changes to its business model.

At the same time, Gazprom has sought to appease the European Commission by offering concessions to try to avert a penalty and a finding of wrongdoing. But sources said the two sides are far apart on the issue of pricing.

The talks would be Alexander Medvedev's second meeting with Vestager and would take place during high tension between Russia and the West over Ukraine, Syria and the country's much-criticized plan to bypass Ukraine and extend its Nord Stream gas link to Germany.

Gazprom, which supplies around a third of the 28-country European Union's gas, will defend its case at a closed-door hearing on Dec. 15, three people familiar with the subject said.

Senior officials from the European Commission, their counterparts from EU agencies, rivals and complainants are also likely to attend.

Medvedev will meet Vestager a few days before the hearing, one of the sources said.

Commission spokesman Ricardo Cardoso and Gazprom declined to comment.

The EC says Gazprom's price formula, whereby the price of its gas is pegged to a number of oil products, a practice known as oil indexation, has resulted in excessive prices in Poland, Lithuania, Bulgaria, Estonia and Latvia.

A source close to the company said the EU charges are based on data from 2009 to 2013, when oil prices were high, resulting in an unfair comparison to Gazprom.