Gareth McAuley, Kevin Lisbie and Jon Walters are all racing against time to be fit for Sunday's derby.
Town skipper Gareth has been sidelined for two weeks with a hamstring injury picked up on international duty with Northern Ireland while Jon limped off in the draw at Bristol City last Monday with an ankle problem.
Blues' current Player of the Year had just returned to the side after sustaining ankle ligament damage against Wolves last month.
Kevin suffered a dead leg at Ashton Gate but is rated the most likely of the three to be fit for Sunday's showdown against the Canaries.
"Jon had a scan on Tuesday and there are indications of bone bruising," Town physio Matt Byard told the Club website.
"We've had discussions with a specialist and will see how Jon progresses over the next two days. He has not been ruled out for the derby. It will probably come down to how he feels maybe as late as the morning of the match.
"We will make a late decision on Gareth as well. He's had two good days of light training and we will step that up on Friday. He is scheduled to train fully on Saturday and we will see how he is from there.
"Kevin has been responding to treatment for a dead leg and hopefully he will be back in full training on Saturday."
Tickets for Sunday's game against Norwich are still available but a crowd of around 28,000 is expected and there are no cash turnstiles on the day. Full ticket details on the Club website.
