Lewis Hamilton admits he was "worried" about Sebastian Vettel after the criticism he has faced this season.

The German has come under fire from critics for the plethora of mistakes he has made and also for his performances compared to teammate Charles Leclerc.

Even the word 'retirement' has been used by some, suggesting Vettel might call it a day, and the Mercedes driver believes such scrutiny had a bad impact on his rival.

“I actually worried about him,” Hamilton told Channel 4 at the Russian GP.

“I do know him very well. We’re part of the same generation and I just know how it is to be on the back foot, having people talk negatively about you, have people write you off and also feel that way within the team that the other guy is getting all the energy.

“I know the psychological turmoil that you go through as a driver and as an athlete. I know Seb has been going through that."

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Hamilton even thinks that a clear shift has now taken place within Ferrari, with Vettel playing a back-seat role to Leclerc.

“His teammate has been on the up. I’ve spoken to super, super high up people who say ‘Seb is written off, that’s him done’," he said.

“But now it does appear they have put all their eggs in one basket [at Ferrari] where Seb used to be the number one driver that they would always choose.

“Now, it appears, for some time that it’s now all Charles and their banking the future on him. I think you will see things evolve over the next year or so that will show you that is the case.”

Hamilton though is adamant that Vettel remains a key part of the team at Ferrari and his recent victory in Singapore, his first in 22 races, highlighted that.

“I would say never underestimate the impact of the driver. That car that has been developed over the years has had nothing to do with Charles. It’s been all Seb’s work with the team," he claimed.

“So just to see him have that win, even though I didn’t win the race, I still felt really good because something good came to someone who is actually a decent person and a super dedicated individual, and is not written off.”