The operation was "the result of an old knee injury suffered while playing softball in high school and normal wear and tear over the years," Freundlich said in an e-mail. He didn't say which knee had been repaired.
Afterward, Hill resumed recording her upcoming Christmas album, Freundlich said. She has also been preparing to perform at the Feb. 8 tribute to Aretha Franklin at the MusiCares Person of the Year event in Los Angeles.
MusiCares is a Recording Academy charity that supports the arts community and music education programs.
"Who has time to slow down?" Hill said in a statement. "Doctors had told me to stay off my feet for a bit and now I'm following their rehab program. I intend to be back better and stronger."
Hill, who is married to Tim McGraw, has won numerous honors including Grammy, Country Music Association and Academy of Country Music awards. Her hits include "This Kiss," "Breathe" and "Mississippi Girl."