The 25-year-old has struggled to settle on Wearside following his £5m move from Birmingham City last summer.
His unhappiness had led to speculation that Wolverhampton Wanderers and West Bromwich Albion were ready to make an offer to sign him.
However, Gardner has insisted that he is now "enjoying" playing for the Black Cats.
"You need a settled team, you have players knowing what they are doing and at the start of the season, to be honest, players did not know what they were doing - I certainly didn't," Gardner told The Journal. "I was not the same player I am now and I was last season. Maybe that was me getting settled, but as I say I am settled now and we are ready.
"I don't know where the talk is coming from because I have never come out and said anything.
"It was hard at the start, but I'm enjoying it now. Playing every week has made a difference and I do feel happy now."
Gardner has scored three goals for Sunderland this season.