Via a YouTube video, the Tinkoff-Saxo leader said: "I've been riding my bike during last 10 days and yesterday was the first day I could climb a mountain pass without knee pain, and that excites me, motivates me and led me to take the decision that I will ride the Tour of Spain."
Contador fractured his tibia and suffered a deep cut to his right knee as a result of a heavy fall on stage 10 of the Tour de France. At the end of July, Contador announced that he would not be taking part in the Vuelta - but he has now reversed the decision.
The Spaniard will come up against fellow Tour crashee, Chris Froome (Sky). Froome came away from the Tour with a fractured wrist after crashing out on stage five of the race and is now aiming to salvage his year with a good ride in Spain.
Contador is sensibly playing down his GC chances in the race, however, saying that he may fight for a stage win 'in the final week'.
Nairo Quintana (Movistar), Joaquim Rodriguez (Katusha) and Cadel Evans (BMC) are among the overall contenders in what is shaping up to be one of the strongest start lists the race has enjoyed for several years.
The 2014 Vuelta a Espana kicks off on Saturday, August 23, in Jerez de la Frontera with a 12.6km team time trial. It finishes three weeks later on Sunday, September 14, with a short 9.7km individual time trial in Santiago de Compostela.
Vuelta a Espana 23 August - 14 September television listing
Team Sky manager Dave Brailsford says they'd like Chris Froome to ride this year's Vuelta a Espana whatever his condition
British Orica-GreenEdge rider Adam Yates to make Grand Tour debut in 2014 Vuelta a Espana
Thank you for reading 20 articles this month* Join now for unlimited access
Enjoy your first month for just £1 / $1 / €1
*Read 5 free articles per month without a subscription
Join now for unlimited access
Try first month for just £1 / $1 / €1