Reedus' rep tells us the actor suffered a concussion Friday on the set of "The Walking Dead" -- although it's unclear if it happened while filming or not. There's also no word, thus far, on what exactly happened and how severe it was.

It couldn't have been too bad, though ... we're told Norman's already been discharged from the hospital, and his rep says NR is "recovering well" and set to return to work soon.

Norman's in the middle of production for what is supposed to be the final season of the long-running series -- this before his own spinoff goes into production, which is expected to start sometime this year or perhaps next.

News about Norman having been injured first broke Tuesday via comic convention the Fandemic Tour, which noted he'd been hurt and had to cancel a scheduled appearance ... without elaborating on what exactly had gone down.

As you probably know ... Norman's been with 'TWD' since the very beginning, and with the offshoots in the works, ya gotta figure everyone's happy to hear he's okay.