The Swans midfielder has not recovered from the hamstring injury he sustained in the opening fixture of the season against Leicester City and so misses the international match at The Liberty Stadium on Friday evening - kick-off 7.45pm.
However, The Swans will have four players in the squad in Shaun MacDonald, who will captain Bryan Flynn's side, David Cornell, Ashley Richards and Casey Thomas.
Wales U21 Squad: Cornell, Maxwell; Blake, Bloom, Eardley, Morris, Ribeiro, Richards, Taylor, Wilson, Matthews; Bradley, Collison, King, MacDonald, Partington, Ramsey; Church, Evans, Thomas, Vokes, Williams.