Mario Gotze says title-chasing managers Pep Guardiola and Jurgen Klopp are both "outstanding coaches".
Borussia Dortmund forward Gotze worked under Klopp during his first spell at Signal Iduna Park, before making a controversial big-money move to Bayern Munich, who were then coached by Guardiola.
City returned to the top of the Premier League with a 2-0 win against Cardiff but Klopp's Liverpool can return to the Premier League's summit with victory at Southampton on Friday Night Football, live on Sky Sports Premier League HD.
In an interview with German outlet Bild, Gotze says he is keenly following every twist and turn in one of the most thrilling Premier League title races in recent years.
"They are difficult to compare because they pursue different philosophies," Gotze said. "The fact is that both are extremely successful.
"I am grateful to have worked with two such outstanding coaches. I watch the games of both teams as often as possible, the title fight in the Premier League is extremely exciting."
Five-time Bundesliga title winner Gotze has shown signs of rediscovering his best form with two goals and three assists in his last five matches for Dortmund, who are two points clear at the top of the table.
The 26-year-old, who has just over a year left on his contract, was linked with a move to Liverpool before leaving Bayern to return to Dortmund in 2016.
Gotze revealed he still remains in contact with his former mentor, who handed him his debut in professional football.
"He [Klopp] knew that I wanted to leave Bayern. Of course, we talked. He knows me very well and that I am always looking for new challenges," Gotze said.
"I often speak to Klopp,. He brought me to the first team when I was 17 and he made it all possible. We never stopped talking."