Navalny, President Vladimir Putin's most prominent critic, was jailed this week for almost three years for parole violations he called trumped up, a case that the West has condemned and which has spurred talk of sanctions.
Russia has accused the West of hysteria and double standards and said the protests over his jailing, in which thousands were detained, were broken up by police because they were illegal.
Navalny is due in court at 0700 GMT on Friday on charges he slandered a World War Two veteran who took part in a promotional video backing last year's reforms that let Putin run for two more terms in the Kremlin after 2024 if he wants.
Navalny described the people in the video as traitors without a conscience and as corrupt lackeys.
Though the charge is currently punishable by up to two years in jail, he cannot face a custodial sentence because the alleged crime was committed before the law was changed to make it a jailable offense, according to Navalny's lawyer.
Navalny said last summer that the case was part of an unrelenting campaign to stifle his political campaign against the Kremlin.
Josep Borrell, the EU's top diplomat, is set to meet Russian Foreign Minister Sergei Lavrov on Friday.
Despite close trade ties and energy interdependence, Russia's political relations with the European Union have been at post Cold War lows since Moscow annexed Crimea from Ukraine in 2014.
On the eve of the talks, the Kremlin said it wanted dialog between Moscow and Brussels to be restored to discuss what it said were many disagreements.