The 22-year-old is on loan at Blues from West Ham and has clocked regular game time for the Championship side.
Birmingham have been pleased with what they have seen from Longelo and are now looking to keep hold of him permanently.
It is suggested that they could pay West Ham a fee of £400,000 to sign the left-back on a permanent basis.
Longelo came through the youth ranks at West Ham, but found pushing his way into the first team to be a tough ask.
He linked up with Birmingham on a season-long loan deal in the summer and has kicked on with his development in the Midlands.
Longelo has made a total of 15 appearances in the Championship for Blues so far this season, scoring once and providing two assists.
He is also able to operate further up the pitch, as a left-sided midfielder.
