The Spanish golfer -- and reigning champion of the Memorial Tournament, which he was again ahead in on Saturday -- was filmed being approached by PGA officials ... who told him he'd tested positive for the virus, which means he'd have to leave the premises and the game entirely.

It made for such a bizarre moment, as there were cameras all around on the course ... and they captured the exact moment he learned about it, which left him looking defeated. Rahm covered his face and then crouched down in disappointment -- before being led off.

The interaction was filmed from at least a couple different angles ... and the second picked up on some audio as well. You can hear Rahm say something that sounds like "Not again" ... seemingly suggesting he's gone through this before during the pandemic.

The CBS anchors who were covering it live had trouble making sense of what had just happened, but they knew some bad news had just been delivered. As Rahm made his way inside ... his crew pushed away photogs who attempted to follow, presumably for privacy.