Although no obvious chassis flaw was found between the Chinese and Spanish grand prix, Red Bull nonetheless put Vettel at the wheel of the winter testing chassis in Barcelona.
"I do think it made a difference," the German declared after the race.
Auto Motor und Sport correspondent Michael Schmidt said further investigations have been taking place at Milton Keynes after Barcelona.
He confirmed: "The chassis he (Vettel) used in the first four races was in fact crooked."
Schmidt said Vettel, the winner of the last nine grands prix of 2013 on the trot, had suspected something was wrong with his car after China.
"A second down (to Ricciardo) was too much. I had not forgotten how to drive," said the German.