The 27-year-old, who scored 17 times in 39 games for the club before joining the Robins last summer, has been linked with a move back to Somerset this week.
And while Johnson would not be drawn on whether or not he had bid for the striker, he admitted the former Bristol Rovers man would be a fantastic addition to their Championship line-up.
"Andy Williams coming back to Yeovil would be a great situation, whether that situation ever comes up we don't really know," he said.
"Somebody has obviously put it out down there which is how it often starts. We're not quite sure if that's in Swindon's mind. It is certainly something that would be quite exciting; to get someone like him back to add to the squad.
"It is certainly nothing we can talk about right at this instance."