Lady Gaga says she is unable to walk and has had to delay concerts on her world tour.
Gaga told fans online: "I've been hiding a show injury and chronic pain for some time now."
"After last night's performance, I could not walk."
Concerts in Chicago and Detroit in the US, and one in Canada will be moved to new dates which have not been announced yet.
The singer has a condition known as synovitis which causes pain in the joints, but should be better in a few weeks' time.