Lady Gaga said she was "heartsick" to postpone four shows after an injury that has left her unable to walk.
A news release said the pop star's performances set for February 13-14 in Chicago, February 16 in Detroit and February 17 in Hamilton, Ontario, Canada, had been postponed.
Gaga took to Twitter to explain, saying she injured herself during a performance some time ago and her condition had worsened, leaving her immobile following Monday's concert in Montreal, Canada. She said she had been hiding the injury from her staff, but could no longer perform.
"I've been hiding a show injury and chronic pain for some time now, over the last month it has worsened," she wrote. "I've been praying it would heal."
Neither Lady Gaga nor the news release specifies what the injury is.
The remainder of the Born This Way Ball tour is expected to continue on schedule, beginning with a two-night stand in Philadelphia on February 19 and 20. Dates for the missed shows will be announced later.