Lewis Hamilton has raised fears among the Formula One fraternity after posting worrying social media messages in which he says he feels like "giving up on everything".
The British superstar, who is on the brink of clinching his sixth F1 world title, missed out on victory at the Japanese Grand Prix last weekend but it is life away from the track which has seemingly upset him.
Hamilton, 34, has recently been vocal on Instagram due to his concerns about the environment and those frustrations have now boiled over.
In his attempts to make a stamp, the Mercedes driver switched to a plant-based diet in 2017 and in September he helped launch a vegan burger restaurant in London.
He wrote on Instagram: "Honestly, I feel like giving up on everything. Shut down completely. Why bother when the world is such a mess and people don't seem to care.
"I'm going to take a moment away to gather my thoughts. Thank you to those of you who do give a damn about the world."
That post, which was deleted five hours later, followed previous messages on his Instagram story in which he urged his fans to go vegan.
Hamilton wrote: "Hey world, I hope everyone's enjoying their day. I'm sad right now with the thought of where this world is going.
"Extinction of our race becoming more and more likely as we over use our resources. The world is a messed up place. World leaders either uneducated or don't care about the environment at all.
"Agriculture farming is the largest pollutant we currently have by over 50 per cent, far more than our travel industry combined. I'm sad to see so many people, even close friends ignore what is happening daily.
"Education is key and we were taught that eating animal products was good for us but we've been lied to for 100s of years.
"It's taken me 32 years to understand the impact I am having on the world and I'm figuring out daily what I can do to play a better part. I want my life to mean something and honestly up until now my life's had no meaning.
"Being a part of the issue is not meaningful. Being part of the solution is and I'm striving to do better.
"I urge you to do some research, find the compassion I know you have within you to recognise what you are contributing to in terms of what you eat which keeps the meat and dairy industry flourishing and therefore deforestation, animal cruelty, our seas and climate decaying on a daily basis.
"Go vegan, it is the only way to truly save our planet today. It can be done so quickly, all you have to do is put your mind to it."
The five-time world champion previously revealed his concerns about the meat industry, and its potential effects on the environment, animal welfare and human health.
He told the BBC in 2017: "I stopped eating red meat two years ago. I have generally been pescatarian for the majority of the year and now I've cut fish. "As the human race, what we are doing to the world... the pollution [in terms of emissions of global-warming gases] coming from the amount of cows that are being produced is incredible.
"They say it is more than what we produce with our flights and our cars, which is kind of crazy to think. The cruelty is horrible and I don't necessarily want to support that and I want to live a healthier life."
Hamilton, meanwhile, will win his sixth championship a week on Sunday in Mexico City if he takes the chequered flag and team-mate Bottas finishes fifth or lower.
But the Mercedes cars have struggled at the high-altitude venue in recent seasons, and Hamilton fears he will have to wait for a title, which will move him to within one of Michael Schumacher's record.
The US Grand Prix follows the round in Mexico before the season's final races in Brazil and Abu Dhabi. Hamilton, 34, added: "For me it has never been a case of wanting to rush things. Valtteri has driven well all year long, and done well, and he will most likely do a very solid job over the next few races.
"So we still have a battle and the fight continues. Mexico is our Achilles heel, our worst race of the year, so it is going to be a tough one for us. The last few have been pretty shocking.
"It going to be very hard to beat Ferrari there. I don't anticipate it will be Mexico where I win it the title."