Matondo was born on Merseyside but settled in south Wales at a young age and signed for Cardiff.
But the 17-year-old joined City's celebrated academy earlier this year and his progress has now been rewarded by Wales U21 manager Rob Page ahead of next month's UEFA Championship qualifier in Liechtenstein.
"His favourite position is wide left and he's got pace I've never seen a player have before," Page said of Matondo.
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"He's exciting when he has the ball and he can get past players.
"I've seen him play at Man City numerous times and he's got a bright future in front of him.
"He can set up and score goals and I think he's ready for that step up into under-21s football."
Wales started their European Championship campaign last month with back-to-back games in Switzerland and Portugal.
They won 3-0 in Switzerland before losing 2-0 in Portugal.
Matondo replaces David Brooks, a scorer in Switzerland, as the Sheffield United striker has been called into Chris Coleman's senior squad for the 2018 World Cup qualifiers against Georgia and the Republic of Ireland.
Squad: Pilling (Tranmere), O Evans (Wigan), Dasilva (Chelsea), Coxe (Cardiff), Harries (Swansea), Poole (Manchester United), Davies (Fulham), Abbruzzese (Cardiff), Rodon (Swansea), Smith (Manchester City), Broadhead (Everton), J Evans (Swansea), Harris (Cardiff), Roberts (West Brom), Thomas (Leicester), James (Swansea), Matondo (Manchester City), Cullen (Swansea).
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