Helen Flanagan, formerly an actress on Coronation Street, recently tweeted that she was "bored" of being in Wales.
Since then, Sinclair has reportedly informed the Swans that he will not be signing a new contract at the Liberty Stadium, which in turn prompted an offer from Premier League champions Man City.
Flanagan's tweet read: "Started to get bored now, been in Wales too long, must take action."
This resulted in a number of replies on the social networking site from fans of the Welsh club, one of which said: "You're the reason he wants to leave Swansea, he'll go to Man City and his career will rot away."
The 22-year-old has since apologised for the tweet, insisting that her words had nothing to do with speculation surrounding her boyfriend's future.
"My tweet wasn't meant to offend or be insensitive to Swansea fans sorry guys! When Scott's on away games I'm on my own in Wales," she said.
Sinclair is expected to join the Citizens before the transfer window closes at the end of the month.