Vuelta a Espana: Favourites' form unknown, says Sir Dave Brailsford

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Sir Dave Brailsford looks back on Britain's success on the track in Rio

Sir Dave Brailsford says doubts over the form of Chris Froome, Nairo Quintana and Alberto Contador will make for an unpredictable and exciting Vuelta a Espana.

The trio are the favourites for overall victory at the season's third and final Grand Tour, which starts on Saturday and ends in Madrid on September 11.

Froome is aiming to become only the third rider in history to win the Tour de France and Vuelta in the same year, while Contador and Quintana are bidding to bounce back from injury and poor form at the Tour respectively.

Chris Froome (right) and Nairo Quintana (left) are among the favourites for victory at the Vuelta a Espana

Brailsford told Sky Sports News HQ: "What happens in the Tour of Spain is quite interesting, because you are never quite sure of form and fatigue through the season, so you are not quite sure of the level of everybody.

"Contador came out of the Tour early. He had his injury, he has freshened up, he has trained specifically for the Tour of Spain.

Alberto Contador left the Tour de France on stage nine due to injury

"Chris went from riding the Tour, all the way to the very end, Olympics and now the Vuelta, so there will be a bit of fatigue in there.

"Quintana didn't perform to the level expected. His form wasn't where it was meant to be in the Tour, and the question for us is, what has he done in the interim? Has he come back, has he freshened up, is he ready to go?

"There's a big question mark, which is what makes it exciting. We're all set to go again and looking forward to it."

Contador (left) has historically got the better of Froome (right) at the Vuelta

Froome's hopes of victory at the Vuelta were dented by the late withdrawal of Mikel Landa from Team Sky's line-up due to a hip injury.

Landa was due to be a key support rider for Froome in the mountains, and may even have mounted a challenge of his own in the general classification.

Brailsford added: "Unfortunately, he aggravated a hip injury and we did an MRI scan. We probably could have started him, but the chances of him getting over that injury in a three-week race were very slim, and we thought, longer-term, that might not be the best thing to do, so we decided to swap him out and give him time to recover and get on top of that."