Watt had a short spell with the Reds when a junior player.
"I trained with Liverpool's youth team and played a game against Wolves, but I was unfit,' he recalled of three days spent down south," he told the Daily Mail.
"They were all a little bit older than me and full-time professionals and I was still playing part-time with Airdrie. I did OK, but nothing special.
"Liverpool were interested again, but Celtic got it done quickly. No other team made a formal bid, but when someone told me about Celtic, that was it - nothing else was in my mind. I got told on the Wednesday and I think I signed on the Friday."