The German was tightlipped on Friday over the Merseyside club's plans to bring in RB Salzburg forward Takumi Minamino in January.
“It was a great experience for me because I had not a great idea about Japanese football before I met Shinji.
“When we saw him on video and signed him from watching him on video, we thought we [knew] but we were not 100 per cent sure.
“When he was part of training for the first time and we went in the dressing room, all the coaches were hugging each other: “oh my God, we got a super player!"
“It was two years only with Shinji and you know it better than I do, [the] attitude of Japanese players is outstanding, workrate outstanding, football smart, technical-wise really good usually.
“The players I saw [are] really dynamic and just nice people, trying to adapt to the different styles was a great experience. I'm still following his career, obviously, still try to [see] how he's doing."