The 25-year-old picked up a thigh injury in their defeat to Bournemouth in November and, missed games against Manchester United, Watford, West Bromwich Albion and Chelsea as Newcastle struggle to maintain their momentum.
Atsu came on by the 64th minute to replace Matt Ritchie when Rafael Benitez's men were trailing the visitors by 2-1, after two goals from Riyad Mahrez and Demarai Gray cancelled out Joselu's fourth minute opener.
Atsu's presence brought additional bite to the hosts' attack as they began to cause troubles to Leicester's defence and finally found a breach by the 73rd minute through Dwight Gayle.
The striker connected a pass from Mikel Merino and shot Newcastle level but when the home supporters were hoping for the match-winner, Ayoze Perez scored an own goal with four minutes remaining to further deepen their relegation troubles.
Atsu came close to equalizing very late in the game but his effort went wide as Leicester picked their third straight win in the league. Daniel Amartey could not make Leicester squad and it is likely the defender will move out during the January transfer window for more playing time.