Espargaro suffered a crash at Turn 9 during Saturday afternoon’s fourth practice session, and skipped the subsequent qualifying session after being taken to the medical centre.
Later it was confirmed the Spaniard had broken his left radius in the impact and will need to travel to Barcelona for further treatment.
It means KTM is reduced to one works rider for the Aragon GP, with recently-promoted test rider Mika Kallio flying the flag for the squad alone.
Kallio is making his first race outing of 2019 in place of Johann Zarco, who was stood down from his race seat with the Austrian manufacturer six races early.
The Finn was ninth-fastest in Q1 and therefore lines up 19th on the grid on Sunday.