Manager Pep Guardiola urged Manchester City to be wary of former City star Vincent Kompany's Burnley when the teams meet in an FA Cup quarter-final at the Etihad Stadium on Saturday.
Kompany played under Guardiola from 2016-19 before leaving to join Anderlecht as player-manager.
He took over Burnley in 2022 and has led them to the top of the second-tier Championship standings on 83 points from 33 matches, a position from which they look poised to earn promotion back to the Premier League a year after being relegated.
Kompany lifted the Premier League trophy four times during a glittering career with City in which he also won two FA Cups and four League Cups. Guardiola says managing against Kompany makes him feel old.
"He was an incredible figure here," said Guardiola, 52. "He is one of the biggest legends I have had.
"On the other side, I'm concerned because when you start to play a game and the opponent on the touchline is a player that you had, you realise how old you are becoming.
"That is a little bit frustrating, but it's nice to see him. He wants to win, we want to win, and we will take it seriously."
Earlier, Guardiola heaped praise on Burnley and said that Kompany was destined to one day succeed him as City manager.
Ahead of Saturday's clash, however, Guardiola sounded a cautious tone, telling reporters: "I said before that it's nice he'll be back, but these last two or three days, I've only been thinking about what they've done this season."
"I'm not surprised at all with the position they have in the Championship," the Spaniard added.
"They're so close to being a Premier League team. They'll be a tough offering as they do incredible things on the pitch. They have a good team and the way they play is exceptional."
Meanwhile, Kompany has asked Guardiola to stop insisting he will one day take over as Manchester City manager.
"He has got to stop saying it!" Kompany said with a laugh. "I am a Championship manager, I don't know what you want from me!
"I think he should stay for another 10 years at Manchester City first and foremost. Secondly, City are competing to win the Champions League, we are competing to win the Championship so I don't think those kind of conversations make sense."