Klopp coached Gundogan while in charge of Borussia Dortmund.
He said today: "He was one of the best players I ever coached.
"In the 2012 season he was unbelievable - playing much like he's playing now. Then he had injuries. I'm not surprised at all by his current form."
Klopp also afforded a joke when asked about the form of City defender Ruben Dias.
He smiled: "That's a really harsh one. You talk about a centre-half? That's not nice."