Sinclair only made three starts in three years as a City player, during which he had loan spells at West Brom and Aston Villa.
One of those was in the Champions League, in Germany against Borussia Dortmund, but he never featured at home in Europe.
The 27-year-old moved to Celtic earlier this month to rejuvenate his career under his former Swansea boss, Brendan Rodgers, following relegation with Villa.
And with three goals to his name so far, he is feeling good about his return to Manchester after Celtic were paired with City, Barcelona and Borussia Monchengladbach.
“It’s going to be difficult, but I think it’s great for the fans,” he said. “We have had Barcelona almost every time we have been in the Champions League and, on a personal level, going back to City will be fantastic.
“It’s not really a point to prove, but being involved in the Champions League is much better for me when I was at City. I was not really involved some weeks but here I feel at home and feel proper involved. It will just be nice to go back and see some old faces and friends.”
A Celtic player with even closer City links is Patrick Roberts, who is free to play against Pep Guardiola’s team despite being on an 18-month loan move.
And Rodgers will have no qualms over pitting the former Fulham winger against his parent club.
“I think it’s absolutely brilliant,” Rodgers said. “It shows Manchester City first and foremost have sent Patrick out to learn and develop, and this is a clear example from the club’s strategy is that they want him to learn.
“The best way for him to learn is to play in this game. It’s a great opportunity for Patrick and it’s great that Manchester City, even in this pressure situation, can see it as a great part of his learning to be available tom play, even though he could make it difficult for them.”
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