The 66-year-old rocker has been having knee troubles for some time and has been undergoing physical therapy in a bid to ease his pain.
However, May admits he may now faces an operation to correct the problem.
In a series of posts on Twitter.com, he writes, "My knee is deteriorating in spite of intensive physical therapy. I'm heading for the knee replacement op (sic)... I have great trust in my knee Prof (doctor). I am in good hands."