Russia (REUTERS) - Belgian rookie Stoffel Vandoorne is set to start Sunday's (April 30) Russian Formula One Grand Prix from the back of the grid after his troubled McLaren suffered more engine problems in Friday's practice.

Honda said the power unit had been changed, with the excessive use of various components translating into a 15-place penalty.

The Belgian is now on his fifth turbocharger and fifth heat motor generator unit (MGU-H) in three races.

The rules allow each driver four power units, made up of six separate elements, to last the full 20-round season.

Vandoorne qualified 17th at the previous race in Bahrain, 16th in China and 18th in the Australian season-opener, with 20 cars on the grid.

McLaren are enduring a miserable season, currently last in the championship and without a point.

Such is the team's plight that Vandoorne's Spanish team-mate and two-time world champion Fernando Alonso will be skipping the showcase Monaco Grand Prix next month to instead compete in the Indianapolis 500 on the same day.

The 35-year-old told reporters on his arrival at the Sochi circuit, after spending the weekend watching IndyCar and having a seat fitting in the United States, that the decision had given him something positive to focus on.

"You reset a little bit your mind and you are again a rookie in a sense, so you start learning things and being very open to engineers' discussions," he said.

"This two weeks from Bahrain to here, instead of re-thinking about the disappointment of Bahrain you have been very busy. So you arrive here with again a motivation to do well and hopefully finishing the race.

"It's good for the head."