The incident happened about 2 p.m. Friday, said Kim Reischling, a spokeswoman for Fort Polk, in a statement to Army Times.
The soldier was listed in stable condition as of Sunday morning, Reischling said.
The incident is still under investigation, she said, and she declined to provide additional details.
Michelle Tan is the editor of Army Times and Air Force Times. She has covered the military for Military Times since 2005, and has embedded with U.S. troops in Iraq, Afghanistan, Kuwait, Haiti, Gabon and the Horn of Africa.