The Black Cats defender has made a return to the set-up after a year on the sidelines and the U21 boss is happy to have the player back
The 21-year-old, who has been capped at U21 and U19 level for the Boys in Green, had been out of action since November 2012 when he suffered a broken leg while on loan at Bradford City.
Remarking on the Cork native's return to the set-up ahead of his side's Uefa qualification clashes against the Faroe Islands and Montenegro, King explained that it was "good" to have the player back.
"It's great for John after being out for so many months," King said. "It's good to have him back available to us. He's a good player and a very good lad to have about the place.
"He's been in touch over the past year, wishing us well before games. He loves playing for his country and has always done well when called upon. I'm delighted to have him back."
King is back at the helm of the U21 team after a spell as interim boss of the senior team and is hoping to resurrect the team's chances of qualification.
After the 1-0 defeat to Romania at home in October, King's team currently sit second from bottom in Group 6, behind Germany, Montenegro and Romania with four games left to play.
"It's not a question of us looking to get back on winning ways. We're just looking to win the next match and then see what happens with the other three fixtures," added the former Derry City boss. "It's a big task but one we're looking forward to."
Ireland U21s host the Faroe Islands in Sligo on Friday November 15 before travelling to Podgorica to face Montenegro four days later.