Koumas salvaged a 1-1 friendly draw against World Cup-bound Ghana in Cardiff on Tuesday night with a stoppage-time header.
The 20-year-old was a second-half substitute alongside teenage Coventry midfielder Kai Andrews and Swansea winger Cameron Congreve, who made his debut after a successful season on loan at Dundee in the William Hill Premiership.
“We finished as a team with less experience but I thought they were top when they came on,” Leeds winger James said.
“It shows the trust the manager has in these young players and we’ve just got to keep pushing to bring them through.
“He sets up in a way that everyone is in a position where they can be themselves.
“He did exactly the same with me. How I can make my game simple and use my strengths? That’s what he does all over the pitch.”
Koumas burst on to the scene with a debut FA Cup goal for Jurgen Klopp’s Liverpool against Southampton in February 2024. But he failed to play a single minute under Klopp’s successor Arne Slot and subsequently had Championship loan spells at Stoke, Birmingham and Hull, helping the latter reach the Premier League this season.