Red Bull Motorsport Advisor has insisted Sergio Perez is doing "the job we expect of him" despite ongoing struggles in F1.
Perez had been pushing teammate Max Verstappen in what looked to be a two-horse race for the Drivers' title after securing two victories in the opening four races.
But a nightmarish run of three races in Monaco, Spain and Canada saw Perez finish only 16th, fourth and sixth with no appearances in the final part of qualifying, despite the qualities of Red Bull's RB19.
The streak of poor form has raised questions over Perez's future with Red Bull, but Marko has pointed out the Mexican remains in position to complete the targets required by the Milton Keynes-based outfit.
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I honestly don't see anyone there
"We take luxury problems seriously," Marko told F1 Insider.
"As far as Perez is concerned, so far, he has done the job we expect of him. He should help secure victory in the Constructors' championship and the current points score proves him right. He's also proven that he can win races when he's at his best."
"The question of whether he's good enough doesn't arise for us because Max is getting better and better, and the question you have to ask is rather a different one: Who would be the alternative?
"Is there anyone who could really challenge Max at the moment? I honestly don't see anyone there."