Martins has undergone surgery after suffering a stress fracture of the leg. The former Newcastle player, on loan from Russian side Rubin Kazan, scored the winner in the shock win over Arsenal at Wembley in February, but he has not played since appearing against Wigan in mid-March.
Blues manager Alex McLeish said: "Oba has had surgery and it's a blow for him and a blow for us and we wish him a speedy recovery."
He added: "He passed his medical and everything was fine for six weeks but then it became obvious something was not quite right.
"The problem has crept up on him during the past month or so and a stress fracture was diagnosed."
Blues were understood to have an option to buy Martins for around £4 million when he made the temporary switch to St. Andrew's.
He will remain at St Andrews until the loan spell expires at the end of May, but it remains to be seen whether the move will now go ahead.
McLeish has made it clear he will not talk about any possible transfer deals until the end of the campaign.
Source: PA
Source: PA