Lingard returned to the United Under-21 fold and helped create Federico Macheda's goal in the 1-1 draw at Southampton on Monday before being sent off for handling the ball on the line.
The 19-year-old livewire made four appearances for the Foxes but Keane's prospects were curtailed by a hamstring injury he sustained when making his City debut against Bolton. The England Under-19 centre-back Keane will link up with Leicester soon when he reaches full fitness.
"It was a tremendous education for Michael," explained Under-21 coach Warren Joyce to MUTV. "He went into his first game at Leicester playing against Kevin Davies and realised some of the things we've been saying to him over a 12-month period. You can't buy that sort of experience to play against people like that."
Nigel Pearson will be able to call upon the United youngsters for a hectic festive schedule that includes six Championship games with the East Midlanders pushing for promotion to the top flight.
Meanwhile, Hull have confirmed that Brady has extended his second stint with the Tigers until the New Year after impressing manager Steve Bruce.