West Brom coach Appleton insists Mattock has future
The former Leicester City fullback has impressed in reserve-team action this season.
"He got into the Leicester team quite young and got into the England side quite young and then got his move here," Appleton told the WBA website.
"We went from the Championship, where he had played most of the games, into the Premier League and it's a different kettle of fish.
"It's a lot quicker and you get punished a lot more.
"He is only a young player and he finds himself in the second season of his Premier League career, albeit he went on loan last year.
"As a player I think sometimes you have to go out on loan to realise what you want and what you're missing.
"He went out on loan at the end of last year, I saw him myself a couple of times and all the reports we had said he did well enough at Sheffield United.
"We've got no problems with Joe."