Former Red Bull driver Robert Doornbos has claimed Christian Horner is 'not happy' with Helmut Marko.
And the 42-year-old also claims there is still 'plenty of unrest' behind the scenes of the F1 side, despite the success they've enjoyed so far this season.
Horner was recently cleared of misconduct by Red Bull, with the Briton always denying allegations of inappropriate behaviour.
He has since overseen the first four races of the new season in Bahrain, Saudi Arabia, Australia and Japan.
Christian Horner is 'not happy' despite Red Bull enjoying a terrific start to the new F1 season
GETTY
Red Bull have enjoyed success so far this term, with Verstappen winning three of the four events.
The 26-year-old was unstoppable on Sunday and won the Japanese Grand Prix, with team-mate Sergio Perez finishing second.
Marko and Jos Verstappen are believed to be keen for Horner to leave Red Bull amid a wider power struggle at the F1 giants following the death of Dietrich Mateschitz in 2022.
And Doornbos has claimed relations between Marko and Horner remain strained and that 'plenty of unrest' is still rife behind the scenes.
"There is still a lot of unrest behind the scenes," he told Ziggo Sport.
"We get the tip of the iceberg through the media, but Marko is not happy with Horner and Horner is not happy with Marko."
Doornbos also claims Adrien Newey has been keen to distance himself from Horner.
The Red Bull engineer has been linked with a move away amid the saga surrounding the team principal.
And Doornbos added: "Everyone thinks he's Horner's best friend but he doesn't want to be involved in this.
"What I've heard is that he won't renew his contract. And that's a big thing, because if he stops at the end of 2025, where does that leave them for the new era?"
Verstappen has also been linked with a move away amid interest from Mercedes.
The Silver Arrows have a seat free for next year, with Lewis Hamilton departing to pursue a new challenge with Ferrari, and Toto Wolff has refused to rule out a blockbuster switch.
Right now, however, it appears Verstappen will stay.
He did, though, refuse to rule out retiring from F1 when his contract with the side runs out in 2028.
"I'm very happy where I'm at, and we want to keep it that way," he said last week.
LATEST SPORTS NEWS:
Christian Horner and Helmut Marko are believed to have a fractured relationship at Red Bull
GETTY
"I have a contract with Red Bull until 2028.
"After that, I first want to see if I even want to continue.
"That’s for me the most important (thing) - it's not so much about where. These kind of things, I don't really think about at the moment."
Horner, meanwhile, wrote on Instagram on Sunday praising both Verstappen and Perez for their performances in Japan.
"A third 1-2 in four races!" he wrote. "Congratulations to all the Team for a perfect response to Melbourne.
Christian Horner has overseen Red Bull's positive start to the new F1 season with Max Verstappen winning the Japanese Grand Prix on Sunday
GETTY
"A brilliantly executed strategy from @MaxVerstappen1 after the red flag, matched with some superb overtaking and performance by @SChecoPerez, ensured we brought home maximum points from Japan and for Honda’s home race.
"Overall, a great Team performance today; fastest lap, a one-two finish, fastest pit stop and leading first and second in The Championship. Next, Shanghai!"
