The 65-year-old rocker underwent arthroscopic surgery to repair ripped cartilage in his knee in December (12).
May had hoped to be back on his feet within weeks but admits he feels disappointed by his slow progress.
He tells Britain's Daily Mirror newspaper, "It's a battle. At the moment I've got to play sitting down. One thing which might stop us 'being Queen live' right now is my knee damage refusing to heal."