Landa breaks collarbone in another Tour of Basque Country crash
Two-time Tour de France champion Jonas Vingegaard suffered lung damage, broken ribs and a broken collarbone on Thursday, while Remco Evenepoel also broke his collarbone in the same incident.
Primoz Roglic, who had been leading the general classification, retired despite not sustaining fractures in Thursday's crash, while Jay Vine, Sean Quinn and Steff Cras were also hospitalised.
Soudal Quick-Step riders Landa and Gil Gelders were forced out of the race on Friday after another crash.
It was a fast day's racing on the 175.9 kilometre run from Vitoria-Gasteiz to Amorebieta-Etxano, won by Romain Gregoire who edged a bunch sprint to the line.
Spaniard Landa, who finished second in the race last year and in 2018, was pictured on a stretcher being put in an ambulance.
The Belgian team said Landa had fractured his collarbone and "will now undergo further investigation to determine the best path for his recovery".
Lidl-Trek's Mattias Skjelmose defended the yellow jersey he inherited after Roglic's retirement with Max Schachmann two seconds behind after finishing third on stage five.
Gregoire edged Orluis Aular in a photo finish to claim his first world tour win.
"I feel incredibly satisfied, it was a super quick day today and I'm super proud to have won," said a delighted Gregoire.
"I had to really fight right until the end, even up to the finish line I didn't know whether I had won, it was a little bit stressful."
The final stage on Saturday starts and ends in Eibar, featuring seven classified climbs over 137.8 kilometres.
Last year Vingegaard crushed his opponents in a carbon copy of the stage, also claiming general classification victory.
The Dane's injuries pose a question mark over his hopes of recording a third successive Tour de France triumph this summer, with the race beginning on June 29 in Florence, Italy.