Formula One motorsport director Ross Brawn believes Sebastian Vettel's mistakes can no longer be viewed as an unfortunate coincidence and are instead proof that the Ferrari driver is "out of sorts".

Vettel's championship chances took another hit at the U.S. Grand Prix on Sunday when he started fifth on the grid due to a penalty and was then involved in a collision on the opening lap with Daniel Ricciardo. He has not won a grand prix since the Belgian Grand Prix in August and now needs to win the remaining three races and hope title rival Lewis Hamilton scores less than five points in the same period.

In contrast, his teammate Kimi Raikkonen won the U.S. Grand Prix after making a strong start from second place and Brawn believes it's time for Vettel to reassess his approach to racing.

"On a weekend on which Kimi demonstrated that the Ferrari was once again really quick, the other side of the coin is represented by Sebastian Vettel, who was again no stranger to mistakes," Brawn said.

Sebastian Vettel is all but out of the championship. TOSHIFUMI KITAMURA/AFP/Getty Images)

"On Friday there was a small one, when he failed to slow sufficiently for red flags, and he paid the price with a three-place penalty. 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, but rather they would seem to indicate that Sebastian is a bit out of sorts at the moment."

Brawn, who was the technical director at Ferrari during its last period of sustained success with Michael Schumacher, believes this year's Ferrari was good enough to win the title.

"It's a shame because this year, the Maranello team has been able to give him a really competitive car -- right from the start of the season. Since the start of the hybrid era, Mercedes has never faced such stiff opposition and has never had to push development as much as it has this year. That's down to the men and women who work at Ferrari and obviously, that includes the drivers.

"Now, any hope of bringing the drivers' title back to Maranello is dwindling and the time has come to do the maths. Their most important task is to work out how to help Vettel make the most of his massive talent. You don't become a four-time world champion for no reason, and Sebastian has definitely not forgotten how to win. In a sport as complicated as Formula One, you only reach your goals if all the pieces of the jigsaw fall into place. If just one piece is missing everything is compromised."