The Australian international limped out of the win over Aston Villa on Boxing Day with a slight muscle tear in his stomach and it was hoped he would be fit by the end of January.
"We did not expect Danny to be out for so long," City boss Kevin Keegan has told the club's official website.
"We hope that he will join in full squad training on Monday."
"We have had him back in two or three times and he just picked up another niggling injury or had the same problem. He has had a real injury disrupted season and has made only ten starts so far."
"His absence cuts down my options on the left hand side and we can't replace like for like."
"Danny is totally different from anything we have at the club. He gives us drive and energy and can get round the pitch."
"He just hasn't been available since Boxing Day when he picked up the original injury."