The 20-year-old was snapped up by United from Valerenga's academy back in 2008 but has struggled to break through as part of a strike force boasting the likes of Wayne Rooney, Danny Welbeck, Javier Hernandez and more recently Robin Van Persie.
Nevertheless loan spells at Preston North End, Borussia Monchengladbach and more recently Hull City have seen moderate auccess and King's stock rise. Newcastle were said to be interested in acquiring his services on a permanent basis back in the summer.
However the majority of his career success to date has arisen from his performances on international duty, where he is now a regular in the Norway national team squad. Last month he grabbed his first goal for his nation, scoring the final goal in a World Cup Qualifying tie against Cyprus, helping Norway to a 3-1 victory.
Clubs would have been on red alert since earlier in the season when King expressed a desire for playing time, saying 'I have set Christmas as a deadline. If I haven't got more playing time by then, I will consider moving to another club'.
It would now appear that King's international performances have attained the interest of new Blackburn manager Henning Berg, keen to make the striker his first signing for the club. The deal will no doubt be helped along by Berg'a connections to United boss, Sir Alex Ferguson, of whom Berg played under for three years between 1997 and 2000.
The striker will be joining an already highly-bolstered strike force at Blackburn where he will have to compete with the in-form Jordan Rhodes, Nuno Gomes, Leon Best, Colin Kazim-Richards, Ruben Rochina and David Goodwillie for a starting berth. Based on the competition already at the club the move will maybe come as a surprise to fans, with other areas perhaps in need of reinforcement more desperately.
Blackburn currently sit in Sixth place in the Championship, just inside the play-off zone and will be hoping that King can add extra firepower to push Rovers towards automatic promotion. With such heavy competition he's certainly going to need to hit the ground running when opportunities arise.
King's five minute cameo against Galatasaray during Tuesdays Champions League tie may now prove to be the last time United fans see the striker in their red strip, if Blackburn invoke a clause that will allow the move to become permanent.
Blackburn fans, is King a good signing for your club? And United fans, is it disappointing to see a young talent leave the club or was he never going to make it with you?
image: © Ronnie Macdonald