Dekker was on the team's preliminary Vuelta squad, but at the beginning of this month it was said that he would concentrate on one-day races instead. But now he is back on for the three-week stage race.
"I said before that I wouldn't be riding the Vuelta because I already completed a hard program this season but nothing changes as fast as the life of a pro cyclist. To get a bigger engine I will have to ride a Grand Tour sooner or later. The past week showed that my form is good enough to start in La Vuelta,” he said.
Dekker, 27, will start Tuesday in San Sebastian, and will remain in Spain to prepare for the Vuelta, which starts with a team time trial in Pamplona on Saturday.
"My trainer Adrie van Diemen advised me to take this chance to ride the Vuelta now. I am ambitious before the race. My aim is to help the team but also to find out where I stand personally. It's been five years since I did a Grand Tour because my last one was the Tour de France in 2007.
“It will be a hard race in Spain but it will help me further. It's my first time ever in the Vuelta a España and I am really looking forward."
Dekker rode the Giro d'Italia in 2005 and the Tour de France in 2007. In 2009 he was given a two-year ban for doping, and he returned to racing last season with the Chipotle Development Team, before moving up to Garmin-Sharp this year. He won a stage at the Circuit de la Sarthe in April.