"Unless Quintana has a bad day, he is the winner of La Vuelta," Contador told Spanish radio Cadena Ser.
Contador is fourth in the general standings, four minutes and two seconds behind Quintana.
Five seconds separate Contador from third-placed Johan Esteban Chaves of Colombia.
To beat Contador and win La Vuelta would be a significant achievement for Quintana, the 2014 Giro d'Italia champion.
"I've had to learn a lot very quickly from figures like Contador," Quintana told Marca. "I followed his movements during an epic stage of his at Fuente De (four years ago) and I said to myself that if I wanted to be someone important in cycling, I would have to learn what a rider like Contador did.
"There is still some way to go."
Tuesday is the second rest day of La Vuelta before the riders go on a 117.5km ride from Castellon to Llucena on Wednesday.
(Reporting by Adriana Garcia; editing by Amlan Chakraborty)
