Like the initial deal, Sunderland have inserted a 24-hour recall clause in the new agreement.
Foxes manager Nigel Pearson told his club's official website: "Sunderland have the recall option but I would rather have the player available than not. He is enjoying it here and we are delighted to have him.
"For a player of his age from a Premier League club this is a good experience for him. Both clubs benefit because he is getting vital experience and we have the services of a player who has a lot of potential."