Moorhouse, 20, has been with the O's since the start of the 2025/26 campaign, initially departing United back in August.
He scored his first goal for the club in a 3-1 win over Peterborough United in the EFL Trophy earlier this term and has been a mainstay in Richie Wellens's side.
Jack has also gained further experience at international level during his short spell away from the club, featuring twice for Northern Ireland's Under-21s.
Playing against England and Andorra in November, Moorhouse has now featured three times for his nation.