Carlos Sainz admitted he was angry with his team after Sunday’s Hungarian grand prix.
Spanish media reports say the 20-year-old was running ahead of his high-profile teammate Max Verstappen when the Dutchman was given the preferential pitstop strategy.
"I’m angry because I was doing a very good race," he was quoted by Marca sports newspaper.
Sainz ultimately retired with a technical problem, but he admitted to being most upset and baffled at why his team appeared to favour Verstappen.
Ultimately, Verstappen finished fourth.
Writing in the Spanish daily AS, correspondent Manuel Franco sensed favouritism.
"It’s not the first time," Franco said. "It’s difficult to fight on equal terms with a driver that they have called the ’new Senna’."
Sainz said: "It has not been explained to me why they didn’t stop me first. Imagine the anger that I have. I stopped later than the others, Max did ’the undercut’ and passed me in the pits. That’s what I cannot understand."