The centre-back, 19, had been part of the Reds' squad which was in Switzerland for a pre-season training camp.
But the former Lincoln City schoolboy will be swapping Anfield for the Walkers Stadium after agreeing a move to the Foxes until May.
Hobbs joined United on loan in January's transfer window, making nine appearances and scoring one goal.
He is relishing the prospect of an entire season of first-team football.
"I want to help this club get back to the Championship at the first time of asking," he told Leicester's official website.
"I can assure everyone that I will be giving 100 per cent. This is a massive club with a good manager and top class Premier League facilities"
Hobbs will make his first return to Glanford Park as a Leicester player on Saturday November 22, while United head to the Walkers Stadium on Saturday April 25.