As a youngster, Carney was on the books of English Premier League club Everton but didn't break into their first team and played for lower division teams Oldham and Halifax and Scottish side Hamilton Academicals, before returning to Australia.
Carney said his A-League stint had been a big help in establishing himself in England.
"I'm more mature as a player, I think when I went over there it definitely helped me and I feel a better player for it," Carney said.
"It was a big year, we had two managers, the Championship is a really hard league to get out of," Carney said.
"It's a massive league, one you don't want to be in, you'd rather be in the Premier League."
United finished seven places above local rival Sheffield Wednesday and ended up ninth, just four points and three places out of the play-offs.