The draw at Old Trafford leaves Ralf Rangnik's misfiring side three points behind the fourth-placed Gunners, who have two games in hand. United, missing top-scorer Cristiano Ronaldo through illness, looked anaemic in attack for most of the first half as they struggled to establish any attacking rhythm.
It was the visitors who took the lead in the 63rd minute when forward Iheanacho headed past David de Gea, who got a hand to the ball but could not keep it out.
Leicester's lead was short-lived, however, with United level just three minutes later. The ball broke for Fernandes after the visitors failed to clear their lines properly and Fred lashed into the roof of the net.