Charles Leclerc and Max Verstappen were in dominant form at the Russian Grand Prix on Friday as the young duo set the practice pace.

Leclerc has turned in excellent performances in recent weeks, winning in Belgium and Italy before seeing Ferrari's pitting tactics prevent a likely hat-trick in Singapore, where he finished second to team-mate Sebastian Vettel.

Meanwhile, Verstappen, the sport's other outstanding youngster, has not quite managed to build upon two wins in three races shortly before the mid-season break.

But the two were at it in Sochi, with 21-year-old Leclerc fastest in FP1 with a best time of one minute and 34.462 seconds.

Verstappen, also 21, split the two Ferraris, which has benefited from recent upgrades that were particularly effective in Singapore.

However, Scuderia sporting director Laurent Mekies, speaking following the session, warned there will not be significant further changes to the SF90 car this year.

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"I think it's that time of the year when we are all switching our attentions to 2020 so I don't think there will be anything significant from now until the end of the season," Mekies told a news conference.

"On top of that, you also need to start thinking about what's going to happen next. So the short answer is there won't be anything significant anymore."

Leclerc and Ferrari were impressive again in FP2, yet they could not match Verstappen this time, as he recorded a time of one minute and 33.162 seconds.

Championship leader Lewis Hamilton struggled to contend on Friday, almost hitting Romain Grosjean in the pit lane as he came fifth in the first session, before improving to fourth in the second.

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However, while Red Bull enjoyed a strong day with Verstappen, sister team Toro Rosso did not fare quite so well.

Russian Daniil Kvyat, who was forced out of FP1 at his home grand prix, made contact with team-mate Pierre Gasly in the second session, immediately taking to the team radio to apologise.

"Sorry, I didn't see him," Kvyat protested, having at least escaped a major collision and serious damage.

The incident came as the possible identity of Verstappen's 2020 Red Bull team-mate continued to lead the off-track agenda.

Both Red Bull boss Helmut Marko and Toro Rosso chief Franz Tost had ruled out Kvyat in the past week, seemingly leaving Alex Albon - currently in the seat - and the man he replaced, Gasly, to battle for the spot.

Verstappen told reporters in Russia: "It's up to [Red Bull]. I'm not the deciding factor and I also don't want to be. I don't mind who is sitting next to me, and they are the bosses so they decide."