Keeper Dean Gerken is set to be out of action for at least a month with the shoulder injury he sustained in the closing stages of Saturday’s 3-0 defeat at Birmingham City.
The 30-year-old collided with James Vaughan and required lengthy treatment before seeing out the game’s final minutes.
"Gerks has seen a specialist in London and had a scan and he has suffered a partially torn ligament in his right shoulder,” physio Matt Byard told the club site.
"He will be reviewed again in two weeks and we are looking at a return at the earliest in four weeks if there are no setbacks in that time. It could be longer.”
In Gerken’s absence, Bartosz Bialkowski will come back into the side with Town's next match against Reading at Portman Road on Tuesday.
Bialkowski played in the FA Cup games with Portsmouth earlier in the month - and was in goal for the Capital One Cup tie at Manchester United in September - but his last league match was the 2-0 home victory over Burnley in August, having also started the opening two Championship fixtures.
Gerken subsequently established himself as Town's number one after Bialkowski was given compassionate leave to return home to Poland to be with his dying father.
Former Wales U19 international Michael Crowe, 20, is currently on loan at Braintree Town and can’t be recalled until February 7th, so Scotland U21 international Jonathan Henly, 21, who joined the Blues in August following a trial, is likely to be on the bench against the Royals, the club who released him last summer.
With neither Crowe nor Henly having played a Football League game, manager Mick McCarthy could look for more experienced cover as he did last season when Gerken suffered a knock and veteran former Sheffield United and Ireland keeper Paddy Kenny joined on a short-term deal.