Mattock backed to rebuild West Brom career
The fullback has earned a surprise recall to the England U21 squad.
Baggies coach Michael Appleton said: "I think it's fantastic for him and it's not the first time he's been with the England set-up. He's pushing the likes of Nicky Shorey, Steven Reid, Billy Jones and others.
"We've got some good full-backs in the squad who are all pushing each other and fighting for places in the starting line-up. And Joe is now part of that."