Manchester United forward Adnan Januzaj failed to show the necessary desire during his loan spell at Borussia Dortmund, coach Thomas Tuchel has said.
Belgium international Januzaj, 20, joined Dortmund on a season-long loan in the summer but the agreement was cancelled this week after making just six appearances for the Bundesliga club.
Tuchel said Januzaj, who was accused of having a "bad mentality" by Belgium under-21 coach Enzo Scifo in November, did not make an impression due to his lack of commitment to BVB.
"I never had the feeling Adnan was here with his whole heart, but rather that a part of him stayed in Manchester and compared everything with Man United," the Dortmund coach told Sport Bild.
"We were not able to help him let go of it. Sadly, he wasn't in it with the motivation and attitude you need to further yourself at this age."
Januzaj will now attempt to establish himself under Louis van Gaal at Old Trafford in the second half of the season, along with Will Keane, who has been recalled from a loan spell at Preston.
Van Gaal told reporters on Friday: "They are coming to us to ask for a second chance and Manchester United is a club that takes care of all our players and I think it's a very good habit to have that.
"I believe in the talent of Adnan Januzaj. I said it would be very difficult to play matches in Dortmund and unfortunately I was right.
"He has been trained already this morning, but he didn't play so many 90-minute matches in one season and he has to show his fitness in the second team.
"We have to wait and see if his [clearance] papers are right. If he can play Monday in the second team [at Reading] he shall play in the second team."
ESPN FC's Germany correspondent, Stephan Uersfeld, contributed to this report.