The 19-year-old is struggling with a cartilage injury and will not make the trip to Baku this weekend.
Confusion reigns as to how the youngster sustained the problem, with the Welsh FA adamant he reported no complaint following Wales' 1-0 victory over Estonia on Friday.
His absence for the tricky trip to Eastern Europe has come as a major blow to John Toshack, who has already seen his squad whittled down to the bare bones.
Craig Bellamy, James Collins, Simon Davies and Jason Koumas are all missing, while Ched Evans and Sam Ricketts have also been forced to pull out.
DoubtsManchester City striker Evans picked up a back injury against Estonia, while Ricketts has failed to shake off a similar injury of his own in time to face Azerbaijan.
Toshack also has doubts over West Ham midfielder Jack Collison, who limped out of the action on Friday.
The youngster has only recently recovered from a knee injury and has suffered a slight recurrence of that problem.
A decision on his fitness will be made on Tuesday morning, prior to the squad's departure for World Cup duty.
Meanwhile, Swansea winger Shaun MacDonald, who has 18 U21 caps to his name, has been called up to provide cover for the mounting absentees.