The defender had major surgery and missed most of last season after suffering cartilage damage but on his return to the line-up the injury got worse before he underwent a clean-up operation last week.
"It was good news for me," Virgo told the Bristol Post.
"The problem was nothing more serious than a reaction from my previous operation. There were a few loose fragments floating about inside, so I've had the knee cleaned out.
"It is frustrating, but it could have been a lot worse. There was a stage when the doctors thought the problem might have been a lot more serious.
"That was a worry. I've got a wife and family and a lot of things went through my mind during what was a short period of uncertainty.
"The knee wasn't 100 per cent right and it gradually started to get a lot more uncomfortable for me with every game I've played. Some days I was struggling to walk to the toilet after games."
