Wales captain Rory Thornton will miss the rest of the World U20 Championship because of a knee injury.
The Ospreys lock, 20, will return to Wales for treatment and has been replaced in the squad by regional team-mate Matthew Dodd.
Thornton was named in Wales' 47-man World Cup training squad and was due to join up following the World U20 Championship.
Wales Under 20s face Ireland on Monday in the fifth place semi-final.
Their final game of the tournament will be against either Australia or Scotland on Saturday, 20 June.