Lady Gaga announced her two concerts scheduled for Wednesday and Thursday at the United Center have been postponed.
Live Nation Global Touring says Gaga is suffering from "severe inflammation of the joints" known as "synovitis."
In a statement, the "Born This Way" singer said, "I am completely devastated and heartsick. I've been hiding this injury and pain from my staff for a month, praying it would heal, but after last night's performance I could not walk. To the fans in Chicago, Detroit and Hamilton, I hope you can forgive me as it is nearly impossible for me to forgive myself right now. I would do anything for you. I will hopefully heal as soon as possible and be at 500% again, which is what you deserve."
Shows in Detriot and Hamilton, Ontario are also shelved.
The dates will be rescheduled, and fans are advised to hold onto their tickets. If needed, refunds for the postponed performances will be available at point of purchase.