He said: "I can tell you that we are hoping to shoot [the reunion] in August, in mid-August, but honestly, we will do it when it's safe. There has always been a hope that a component of that reunion show will have a live audience, which makes the whole thing really tricky. We are obviously not going to risk anyone's health by doing this."
The one-off programme will see him back together with former co-stars Matt LeBlanc, Jennifer Aniston, Courtney Cox, Matthew Perry and Lisa Kudrow.
The comedy's co-creator Martha Kauffman had suggested filming could happen in August.
She explained: "We are hoping to be able to shoot in August, if all is well and there is no early second wave and the studio is open. If everything is in place and we understand all the protocols and we can still make a good show, we'll be shooting it some time, mid-to-late August."