Sebastian Vettel will incur a five-place grid penalty at the Russian Grand Prix following an unscheduled gearbox change on his Ferrari.

Vettel endured frustration in Sochi on Friday as a suspected electrical problem brought a premature end to his participation in the second free practice session, in which he was second fastest behind champion Lewis Hamilton's Mercedes.

And a further setback followed for the four-time world champion as Formula One's official website confirmed he will be penalised ahead of Sunday's race.

Reflecting on his practice problems, the German said: "It is a bit of a shame, as we are now missing quite a few laps especially for the long runs and in the race trim. This would have gotten us much more information on how competitive we would be on Sunday.

"Kimi [Raikkonen] had to do the homework for the whole team and that was not too bad, as we roughly know what to expect, and for sure we can also learn from what other people did.

"The good news is that the balance of our car feels quite good and the track is suiting us more and more. But still I have to say that we are not the favourites here.

"We have already seen that [Mercedes] are again very strong here and especially Lewis [Hamilton] got very well into the rhythm."

Vettel sits fourth in the drivers' championship after claiming two podium finishes in the first three races of the season.