Town have confirmed that former West Ham midfielder Jack Collison has signed a short-term deal until late December.
The 25-year-old has recently spent time training with the Blues and also at Birmingham City and was offered the terms a fortnight ago.
"I offered him a deal, I think he’s going to sign it and it’ll take him until just before the next window," manager Mick McCarthy said.
"You don’t have to have too many missing through tiny little things for one game and having another extra body of his quality will be nice to have around.”
The Blues boss says the Wales international won't be involved in the squad for Saturday's game against Rotherham: "No, next week.”
Watford-born Collison played youth football with Peterborough and Cambridge before joining West Ham’s set-up.
He made his senior debut in January 2008 and went on to make 87 starts and 34 sub appearances, scoring 14 goals while at Upton Park. The 6ft tall midfielder was on loan at AFC Bournemouth and Wigan last season.
After leaving West Ham in the summer - and writing an open letter to supporters - Collison spent time on trial at QPR and played in a number of their pre-season friendlies before joining the Blues squad for training at Playford Road in mid-August.
Qualifying for Wales via his grandfather, Collison has won 17 full caps without scoring an international goal.
Collison, who has already appeared for Town’s U21s on a number of occasions, will wear the number 31 shirt.