Sinclair, who represented Great Britain at the Olympics earlier this month, revealed he wouldn’t be signing a new contract at the Liberty Stadium as he enters the last year of his deal.
The 23-year-old played a key role for the South Wales club last season scoring eight times as they finished their first season in the Premier League comfortably in mid-table.
City are plotting bids for a number of the countries leading young talents and the former Chelsea man is thought to be high on the shopping list of Roberto Mancini
And Curtis has conceded that Sinclair is now bound for the Etihad Stadium but say he will leave with the Swans best wishes after an impressive two-years at the club.
“(He is) not really interested in signing a new contract and I think Man City have made a bid,” he said.
“So it’s just a matter of time now before it happens and it’s good for both parties. He’s been terrific for us, to be fair, we’ve had two seasons out of him and he was superb in the Championship and virtually his goals got us promotion.
“And last year as well he wasn’t maybe quite as effective as he was his first year – obviously it was a lot tougher opposition – but he’s been absolutely magnificent.
“Like Joe we wish him all the best, but as long as the club keeps pushing forward that’s the main thing.
“It obviously gives Scott the chance to settle in at his new club and it gives us the opportunity to buy a replacement for Scott.”
Swansea boss Michael Laudrup, who led his new side to an impressive opening day victory against QPR, is thought to be lining up Valencia attacker Pablo Hernandez as a replacement for Sinclair.