Ferrari fitted Vettel’s car with a new chassis for the Spanish Grand Prix after discovering a fault following this month’s second race at Silverstone.
He admitted his SF1000 was still “up and down” in the wake of qualifying in Montmelo, where Lewis Hamilton took pole for Mercedes.
Binotto said there was no single reason for Vettel’s woe, which has threatened to push him towards retirement from F1.
“I don’t think there’s a direct explanation for it,” said Binotto. “If there was, we’d have done something about it.”
Vettel sat a lowly 13th in the World Drivers’ Championship standings prior to the Spanish Grand Prix, with Leclerc up in fourth.
Ferrari, meanwhile, were third in the constructors’ table, behind runaway leaders Mercedes and second-place Red Bull.
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