Pep Guardiola has said he knew Cole Palmer was "a star player" but couldn't promise the forward enough game time at Manchester City before his move to Chelsea.
Palmer left City in a £42.5 million ($53.5m) deal last summer and has since become a key member of Mauricio Pochettino's squad at Chelsea, scoring 10 Premier League goals in 20 appearances.
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The 21-year-old, who made his England debut in November, returns to the Etihad for the first time on Saturday.
Ahead of the game, Guardiola said he always knew he was destined for the top.
Asked if he knew Palmer would be a success at Chelsea, Guardiola told a news conference on Friday: "If he plays regularly, yes. I didn't have any doubts about his quality.
"The way he's playing is a star player. He wanted the minutes, it was a question of time to show his immense quality."
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Guardiola has confirmed Jack Grealish will miss the Chelsea game because of the groin injury he picked up in the 3-1 win over Copenhagen in the Champions League. Bernardo Silva, who also limped off at Parken Stadium on Tuesday, is a doubt but is expected to train on Friday.
"All I know is that he [Grealish] is not available tomorrow," Guardiola said. "Bernardo, we will assess in today's training session. Mateo [Kovacic] is back in training, Sergio [Gomez] as well -- the rest we will see."
City face Chelsea on the back of an 11-match winning run in all competitions, while Chelsea have won their last two against Aston Villa and Crystal Palace following heavy back-to-back defeats to Liverpool and Wolves.
Pochettino has struggled to get any consistency out of Chelsea with the team languishing in 10th on the table, but Guardiola is expecting a difficult evening on Saturday.
"They are an exceptional team," he said. "One of the toughest games we have before the end of the season. In the last games, they play really good. They have everything. They are a really good team, it's a tough one."