Jake Carroll is out of the rest of the season after the Motherwell left-back suffered an Achilles injury that requires an operation.
Carroll, 28, came off during Tuesday's Scottish Cup replay defeat by St Mirren and could miss the start of next season, says manager Stephen Robinson.
However, striker Christopher Long is fit again and midfielder David Turnbull is "not far away", says Robinson.
Peter Hartley and Declan Gallagher are back in training following illness.
Hartley came off at half-time against the Buddies but fellow defender Gallacher and Long have not featured since 12 February.
Turnbull, who came close to joining Celtic last summer before failing a medical, has had preventative knee surgery and Robinson said it "brings a big smile to my face when I watch him in training".
"He is full training, he has played 11 v 11, so we are just waiting for the final OK. I can't wait for that," added the manager.