The Spaniard suffered a broken vertebra and rib when he crashed during the Clásica San Sebastián at the end of July, and his participation at Worlds has been in doubt ever since.
He was ruled out of the Vuelta a España, but was tentatively included in Spain's provisional plans for Worlds, first in a long-list and later in the final seven.
On Wednesday he raced the Giro della Toscana, where he told Cyclingnews he'd wait to see how he felt in the race, and again at the Coppa Sabatini before making a final decision. However, dropped early in the race, the answer came sooner than thought.
"He contacted the national coach, Javier Minguez, to tell him that he still didn't have good feelings on the bike," read a statement from the Spanish Cycling Federation confirming Landa's absence.
Omar Fraile will take Landa's place in the Spain team. While seven of the eight members of were set in stone earlier this week, the Astana rider was down as a reserve, his position dependent on Landa.
"A month ago, when the team was being considered, I didn't want to say no because there was still time to see how I recovered," Landa had said at the start of the Giro della Toscana. "I've trained hard in recent weeks but I had almost a month without making any major efforts."
Spain's team is set to revolve around Alejandro Valverde, who is looking to finally turn his six podium finishes into a gold medal. The hilly nature of the course will suit the multiple Liège-Bastogne-Liège and Flèche Wallonne champion, who won two stages and was in contention for the Vuelta a España title this month before fading to fifth overall on the final mountain stage.
The team also includes Enric Mas, Ion Izagirre, Jesús Herrada, David de la Cruz, Mikel Nieve, Jonathan Castroviejo.