Vettel was neck-and-neck with Lewis Hamilton at the summer break and the Ferrari was considered the quickest car.
However, Hamilton won six races out of the following seven races to leave Vettel in his wake.
The Brit should have wrapped up his fifth world title last weekend at the US Grand Prix, especially when Vettel was hit with a three-place grid penalty, but the Mercedes man was beaten by Kimi Raikkonen.
Hamilton needs just five points more than his rival at the the upcoming Mexican Grand Prix to secure the honour for a second consecutive year.
And Brawn reckons it is no longer a coincidence that the German fails to perform time and time again.
“On Friday there was a small one (mistake), when he failed to slow sufficiently for red flags, and he paid the price with a three-place penalty,” said Brawn.
“Then, in the race, he yet again collided with a Red Bull, this time Ricciardo’s, and once again Vettel came off worst.
“It was another lost opportunity to close the gap in the title fight, especially when we saw what Raikkonen did with the same car.
“I certainly don’t want to put Vettel in the dock, but these incidents can no longer be seen as coincidence.
“Rather they would seem to indicate that Sebastian is a bit out of sorts at the moment.”
Vettel has come under mounting pressure because of his failure to win a world title in his four years at Ferrari.
The criticism has got that bad that Hamilton posted a message on his Instagram sending his support to his rival.
But Brawn thinks Vettel still has the ability to add to his fifth Drivers’ Championship, if given the time.
“Now, any hope of bringing the drivers’ title back to Maranello is dwindling and the time has come to do the maths,” Brawn added.
“Their most important task is to work out how to help Vettel make the most of his massive talent.”
Source : EXPRESS