The South Korea star returned to the BayArena, home of his former club Bayer Leverkusen, our opponents in MD3 of the Champions League on Tuesday night (7.45pm).
In-form Sonny - named Premier League Player of the Month for September - played for the Bundesliga side between 2013-15, scoring 21 goals in 62 games before joining us in the summer of 2015.
Sonny faced the media before training at the impressive stadium in Leverkusen.
Asked how it felt to be back, Sonny said: "I was here for two years and had a very good time. I must say, I felt a little nervous coming back! I'm happy to come back and play against Leverkusen. When I heard the draw I felt some excitement and I'm looking forward to this game."
Below: Sonny in training on Monday night