Blues boss Garry Monk has triggered the clause to recall in-form striker Greg Stewart and bring him back to St Andrews in the current transfer window.
This news comes as a major blow for Scottish Premiership side Kilmarnock, who are only one point behind Celtic and Rangers.
The 28-year-old has been a major key in their success so far this season, scoring eight goals with the same amount of assists.
Stewart is out of contract this summer and with Sunderland expressing their interest already this window and with the embargo still looming, Blues will want to cash in on the Scotsman now before letting him go for nothing in the Summer.
He will finish training up North and return to St Andrews on Monday. Original source: The Scottish Sun