Dr Helmut Marko broke "promises" to Pierre Gasly in 2019, the French driver claims.

Gasly, 23, had a fraught 2019 season, as he underperformed initially for Red Bull's top team and was relegated back to Toro Rosso, where he thrived.

"There are some things that must stay between the team and me," he told France's L'Equipe.

Gasly was replaced by British-born Thai rookie Alex Albon after the summer break.

"F1 is a ruthless world, where there is sometimes a lot of money and politics," said Gasly. "It would be naive not to take into consideration everything that goes into these decisions."

Although not on bad terms with his bosses and retained by Toro Rosso for 2020, Gasly said he was "disappointed" and "upset" about the way the situation unfolded.

"Helmut promised me things, especially changes to the (Red Bull) car," he said.

"He also told me that I was going to stay until Abu Dhabi. Some promises were not kept.

"I was disappointed with all that, but I also know that in F1, it's not just performance that counts," Gasly added.

"There are some things that I could have done differently too. But I'm only 23 and I still have the ambition to be world champion one day, so I take everything that happened with me this year as a lesson."