Nibali was close to joining Team Sky back in 2010 but ultimately decided to stay with Liquigas. He joined Astana this year and went on to win the Giro d'Italia and finish second behind Chris Horner at the Vuelta a Espana. In 2012 Nibali was Team Sky's biggest rival at the Tour de France, finishing third overall behind Bradley Wiggins and Froome.
Nibali has confirmed he will target the Tour de France in 2014 and Astana is building a team to take on Team Sky, setting up a duel between two of the sports biggest teams next July.
"Nibali is our main rival. I've no doubts about that after seeing the route of next year's Tour de France," Brailsford told Gazzetta dello Sport.
"The thing I like about Vincenzo is that he's a real racer. He's a fighter, he's aggressive and never gives up. He can transform a stage into a trap, he's creative and courageous."
"He always gives 100%. You can see his talented and has a modern way of racing. Just think what he can do on the difficult stages and there are a lot of them. On the pave where he's definitely better than Froome. I've seen him ride on the dirt roads at the Giro and then look how good he is on the bike on the descents when it rains."
Brailsford and Team Sky intend to carefully analyse the Tour de France route before deciding on their race strategy and nine riders for the race.
"Nibali is the most complete of Chris' rivals. He could take advantage of the position of the only time trial because it's on the penultimate day," he said.
"The race tactics will change completely and mountain stages will be talked differently. You can't wait too much, you'll have to take risks, It'll produce an aggressive race that will be spectacular for who watches it and so excellent for our sport."
Brailsford is convinced that Froome has to secure victory in the Tour de France by taking time on his rivals in the mountains.
"I've always believed that Chris is much more of a climber than a time trialist and so he's got to gain time in the mountain," he said.
"That will be his mission, without waiting for the time trial. It'd be too risky to put everything on one day. There are five mountain finishes and Froome certainly isn't penalised by that."
Will Wiggins ride the Tour?
Brailsford was diplomatic about Wiggins riding the Tour de France in support of Froome in 2014. However he would like as many British riders in the starting nine as possible for the Grand Depart in Yorkshire but insisted the most important thing is to in a third consecutive Tour de France.