The 27-year-old damaged an ankle tendon during the PRO12 match against Edinburgh in November.
His injury was reviewed this week and the team say although he is making progress, there are still some minor issues.
Ferris is due to be assessed again later this month but it is thought he could need further surgery.
The injury is also casting a shadow on his place in this year's Lions tour.
Meanwhile Mark Anscombe has made 11 changes to the Ulster side facing Glasgow on Friday.
Paddy Wallace is stepping in at fly half for Paddy Jackson, who is making his Ireland debut this weekend.
Neil Walsh and Conor Joyce will make their first starts for Ulster, while Andrew Trimble and Stuart Olding are in the centre. The side will be captained by John Afoa.