The rock veteran had an operation to correct a chronic problem on 6 August (13) and he was discharged from hospital three days later (09Aug13) to continue his recovery at home.
May has been largely absent from his Twitter.com page since the procedure, but he returned to the site on Tuesday (20Aug13) to tell fans he is getting back to work.
The 66-year-old rocker tweeted, "Folks, an apology for absence. This knee replacement journey demands a lot of patience and attention. I had to turn off, and 'do' recovery... Thanks again for the great supportive messages. I'm on the mend, slowly but surely. It's a journey, for sure. First day back at work today."
May is heading into the studio to record with his longtime collaborator Kerry Ellis.