Kepa was drafted alongside striker Rodrigo Moreno, midfielders Pablo Fornals of West Ham and Carlos Soler of Valencia, Villarreal’s Raul Albiol as well as Celta Vigo’s Brais Mendez, who were brought in on Monday.
On Sunday, Busquets left the team’s pre-Euro 2020 training camp while the rest of the squad tested negative.
“Kepa will land this afternoon in Madrid and will join training tomorrow,” the federation said.
“The rest of the players will begin to exercise today at 11:00 (local time) in Las Rozas under the command of Luis Enrique,” it said.
The squad will be given coronavirus vaccines on Wednesday, Spain’s Minister for Education, Culture and Sport Manuel Rodriguez Uribes said later.
Spain continue their warm-up for the European Championship with a match against Lithuania later on Tuesday.
They will line up with a side mainly made of players who featured in the recent European Under-21 Championship and coached by youth team boss Luis de la Fuente.
Their first Euro 2020 match is against Sweden on June 14 and Enrique has until Saturday to make changes to his squad ahead of their opening fixture in Seville.