Per United's Twitter feed, the Portuguese confirmed the 31-year-old will be in his squad to face Hull City at home in the Premier League on Wednesday:
The versatile winger had previously been linked with a loan departure from United—West Bromwich Albion were reportedly interested—as he has had a limited role under Mourinho in 2016-17, per James Nursey in the Mirror.
Young has started just two games in the Premier League this season—once as a right-back and once as a left-winger—and three times in cup matches, per WhoScored.com.
It is likely Mourinho sees Young as a useful squad player as he can be deployed in a number of different positions on the pitch and excels both defensively and going forward.
United are still in three cup competitions—the UEFA Europa League, FA Cup and EFL Cup—and remain in the hunt for a top-four spot in the Premier League.
If the Red Devils are to make a success of the 2016-17 season on a number of different fronts, Mourinho will have to rely on his entire squad to contribute.
Young is contracted to United until 2018. He has been at the club since he moved from Aston Villa in 2011 and has won a Premier League title and an FA Cup with the Red Devils.
He is not one of Mourinho's best starting XI, far from it, but the United manager clearly believes he has a role to play in the second half of the current campaign, and Young will likely be eager to prove his continuing worth at the club.