Douglas Mason, Getty Images
Few details were available as of Saturday afternoon, but venue marketing director Jenny Holmes told West Virginia's WOWK TV that a makeup date will be announced as soon as possible.
The 76-year-old 'Coal Miners Daughter' singer underwent knee replacement last month. Prior to her surgery, the resilient "First Lady of Country" played through the pain at a concert in Buffalo, N.Y., earlier this year, asking the audience's permission to sit down. She also took the stage in 2009 just days after a bout with the flu.
Watch 'Portland, Oregon'