While Leclerc took an emotional victory for Ferrari at the Italian Grand Prix last weekend, Vettel's Monza weekend fell apart after qualifying fourth and then spinning out of leading contention, hitting Lance Stroll and taking a penalty which left him 13th at the chequered flag.
Vettel was less than impressed after qualifying at Monza, where Leclerc was not in position to tow him at the end of a chaotic Q3 period, which saw the Monegasque keep hold of his provisional pole position, earned with a tow from Vettel, as only Carlos Sainz set a time at the end of the segment.
Ferrari team boss Mattia Binotto said Leclerc was "forgiven" after winning the race, and Berger says Vettel cannot play the team game if his colleague is not returning the favour.
"I have to say it clearly: there is no team play at this level in Formula 1," Berger told Kolner Express.
"Everyone is on their own and has to get his own nose in front.
"I do not know if he fooled Vettel, but it has long been clear that Leclerc has an absolute killer instinct and is headed in the direction of the world title.
"That was not so surprising for me. For me it was rather incomprehensible why Sebastian waited so long and did not go alone hunting for pole.
"Without the slipstream, he might not have beaten Leclerc's time but he might have finished second or third. He can never rely on Leclerc."
Asked if Vettel had been naïve, Berger added: "Let's not call it naive, but he has too much good faith. And good faith has little place in top-level sport, where the World Championship is concerned."
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