Valtteri Bottas is to take a five-place grid drop at the Japanese GP for an unscheduled gearbox change.

The demotion means that the Mercedes driver will not be able to start Sunday's race, live on Sky Sports F1 and underway at 6am, no higher than sixth on the grid.

It is the latest setback to have befallen the Finn who has endured a desperate run of form since the summer break and last week described his slump as the " most difficult time of my career so far".

Japanese GP Practice: Vettel ahead of Hamilton on rain-hit Friday

Rosberg joins Sky F1 in Japan

In Friday's dry running at Suzuka, Bottas was once again over half a second slower than world championship leader Lewis Hamilton in the sister Mercedes.

"My run with the soft tyres was good but with the supersoft I didn't really gain any grip," said Bottas. "The car did feel better than it did in Malaysia but we still need to work on things to make the car quicker."

Hamilton - who, like Bottas, ran the new aerodynamic package which Mercedes introduced in Malaysia - was quickest of all in Practice Two. But with heavy rain falling, only five drivers set a timed lap.

"The car feels back to normal, so l am ready to race," Hamilton said. "The car felt massively, massively different to the last race.

"But Ferrari had some impressive pace. We're strong and hopefully we can compete with them."

Ted Kravitz gives his advice on where to go and what to see in Japan this weekend, supported by FairFX - Sky Sports F1 sponsor Ted Kravitz gives his advice on where to go and what to see in Japan this weekend, supported by FairFX - Sky Sports F1 sponsor

However, Hamilton was angered by the lack of track running with the majority of the field restricted to installation laps in the afternoon session due to the persistent downpour.

"We have this silly rule where you only have a few tyres," Hamilton told Sky F1. "And then there are people sitting in the grandstands all day waiting for us and all they see is three [sic] cars going out.

"It is a silly, silly rule. I feel like we rob them and they should get their money back."

Watch the Japanese GP LIVE ONLY on Sky Sports F1 this weekend. The race from Suzuka begins at 6am on Sunday. Want to watch but not got Sky F1? Buy a NOW TV pass from £6.99!