An adult lion at Chicago's Lincoln Park Zoo (search) attacked an animal keeper Thursday, injuring her seriously before fellow workers could shoo the beast away, officials said.

Nancy DeFiesta suffered injuries to her back, neck and arm during the attack, which occurred during her routine morning work on the lion exhibit, said Kathryn Gamble, chief veterinarian for the zoo.

Chicago Fire Department paramedics transported DeFiesta to Illinois Masonic Medical Center (search), where she was listed in serious condition Thursday afternoon.