Former Santos attacker Roger collapsed on the field during a Paulista Championship match on Sunday.
The 26-year-old Oeste forward remains in intensive care after passing out in the final moments of the club's clash with Ituano at the weekend.
The player is understood to have been transferred to the intensive care unit of the Santa Casa hospital in Itapolis, according to Globoesporte, and will undergo a series of tests.
Oeste director of football Mauro Guerra stated: "Roger is always undergoing endoscopy tests on his throat to make sure he can play, and to check on his health.
"As he had not been playing in our most recent games and the heat was hellish here in Itapolis during the game, that could have caused his collapse."