"He is a bit different to what we have and I think he will be a good addition," said boss Ian Sampson after agreeing a deal for the 20-year-old with parent club Leicester City.
Sampson has often talked about his desire to have another option up front at his disposal and has been backed in the transfer market with the money generated by the club's cup runs this season.
King will go into the squad for Saturday's attractive looking Sixfields clash with Port Vale.