The 22-year-old has finalised fresh terms with the Reds that will run until June 2025, with the option of a further year.
His immediate future, however, lies away from Old Trafford as a temporary move to Sparta Prague has been secured, subject to international clearance.
Earlier this year, he moved to Burton Albion for a similar spell.
Everyone at United would like to wish Matej the very best of luck during his loan spell and we will keep tabs on his progress.