As a result of the left-back's lay-off, Paul Robinson has had his current Blues deal extended until January 27.
Murphy limped off during last Saturday's home defeat to Hull City and will now go under the knife to discover the full extent of a cartilage problem
Of even greater concern to Blues boss Lee Clark is the fact that the worst case scenario could see the 28-year-old out of action for five months.
The loss of Murphy comes on the back of long-term injuries to defenders Stephen Carr (knee) and Paul Caddis (shoulder). Pablo Ibanez has just recovered from a broken foot and Curtis Davies is still undergoing treatment for an ankle problem.
“We won’t know exactly what the situation is until Murph has had the operation on Thursday evening,” said Blues boss Clark.
“He’s damaged his cartilage and it could be anything from six weeks to five months. Obviously we are hoping that it is not very serious because we all know he’s a very important player to us. We will have to wait and see.”
Robinson will now remain at St. Andrew's for an additional two months having recently played a major part in Clark's plans. Since joining the club in September, the former West Bromwich Albion and Bolton Wanderers player has made eight appearances. Although he is predominantly a left-back, he has recently been used as both a right-back and centre-half.
Clark has been delighted with Robinson's commitment and he feels he is a valuable asset to the club both on and off the field with the experience he brings.
“I think we have all seen how well Robbo has done, and in three different positions,” added Clark. “Since coming in he has played an important part for us and been very consistent in his performances.
“We were always looking to extend the contract for a longer term and obviously with Murph now having surgery, he’s going to remain a vital player for us.”