The 46-year-old was knocked unconscious after slipping and hitting his head on a small goal that he was carrying, according to a statement released by the club.
Galtier was left with a deep gash to his right cheek, but subsequent hospital tests are said to have proved "reassuring".
"This morning, after the workout, Christophe Galtier slipped on the ground carrying a metal mini goal. The coach of ASSE, whose head hit the goal, suffered a head injury which resulted in a loss of consciousness," said a club spokesperson.
"Suffering from a deep wound in the right cheekbone, he was immediately supported by the medical staff of the club and then by firefighters and ambulance personnel. Additional tests performed at the hospital proved reassuring."
St Etienne's are in Ligue 1 action this Friday when they take on Toulouse away from home.