The 27-year-old Brendan Rodgers signing spent three years at the club before moving to Aston Villa last season.
But he insisted he won’t have a point to prove against his former employers.
“It’s going to be difficult, but it’s great for the fans. Obviously, we have had Barcelona nearly every time we have been in the Champions League, so that will be great and going back to City on a personal level will be fantastic for myself.
“I don’t really have a point to prove, but being in the Champions League and being involved is much better on a personal level than when I was at City. I wasn’t really involved for some weeks, but I feel at home here and properly involved and I can’t wait to get started.
“It will just be nice to go back and see some old faces and friends, but the club has evolved. They’ve got new players and a new manager. In football, things move on so quickly, but there are a few faces I still know, so it will nice to go back and play against them.”
Sinclair added: “As a player and as a team, you go out there to try and win – that’s the main thing – but I don’t think we have much pressure on us.
“No group is easy. You get the big teams in the Champions League and all the group stages will be difficult, but to have Barcelona and Manchester City will make it very difficult. However, we just need to play our game and enjoy it.
“Opposing players have said how hard it is to come to Celtic Park and it will be very difficult with the amount of fans right behind us, creating that atmosphere which will be unbelievable.”