However, that misfortune may have worked in the Tigers' favour, with competitors for the defender's signature unlikely to make a move for him while he is not fully fit.
He told the Yorkshire Post: "There is every chance I could go back to [Hull] City and if that was to happen, I would welcome the chance to play my part in helping the club avoid relegation.
"Stuart Pearce told me at the start of the season that I was free to find another club and that is still the same situation.
"I came close to moving to Blackburn Rovers last summer until the deal fell through at the last minute and my main aim is to keep playing in the Premiership for as long as I can.
"But obviously the injury is going to hamper my chances of playing in the top flight again in the short term so there is no way of knowing what may pan out during the January transfer window.
"So there is every chance I might have to drop down a level to the Championship, which would not be a problem for me at all.
"I am happy living in Yorkshire and would want to play for a club in the north. I would like to think there is a good chance I might end up back at Hull."
Mills played 9 times for Hull City while on loan from Manchester City this season.