But Bath believe that Catt and Balshaw could be involved in the top-of-the-table English Premiership clash against Wasps on February 7 - eight days before England's opening RBS 6 Nations appointment with Italy in Rome.
"Mike is rehab-ing well from hamstring and calf problems related to lower back problems," said Bath fitness chief Chris Mallac.
"He is feeling fit, and should be back within the next two weeks ready for Wasps.
"Iain's calf injury is resolving now. He is almost back to full training, and has participated in a few light sessions.
"He needs a few more weeks to pick up his speed, fitness and strength. He will be fit to play against Wasps."
Catt and Balshaw are among nine members of England's World Cup squad currently sidelined, joining their club colleague Mike Tindall, who should return from an ankle injury in late February, Jonny Wilkinson, Matt Dawson, Richard Hill, Julian White, Lewis Moody and Martin Corry.
England head coach Sir Clive Woodward is likely to announce a RBS 6 Nations squad next week, after updated fitness checks are carried out on the sizeable injured contingent.