Ajax manager Erik ten Hag has accused Manchester United of committing a "mortal sin" with their treatment of Donny van de Beek.
United invested £35 million ($46m) in Van de Beek's talent in September 2020, prising him away from Ajax on a five-year contract.
The Dutchman was initially heralded as a stellar signing after his rapid rise to prominence at Johan Cruyff ArenA but has found regular opportunities hard to come by at Old Trafford, much to the bemusement of Ten Hag.
What's been said?
Three of Van de Beek's five years at Ajax were spent under Ten Hag, with the midfielder playing a crucial role in their run to the Eredivisie title and Champions League semi-finals in 2018-19.
The 24-year-old's former manager thinks United have held back his development over the past 14 months, as he told De Volkskrant: "Take Donny. I find that hard, a mortal sin.
"If you haven’t had a chance yet, then development will also stall."
Ten Hag added on Van de Beek's struggles in Manchester serving as a cautionary tale for the next generation of young players at Ajax: "Everyone understands that as a top athlete you want to push your limits. If you don’t have that mentality, then you don’t belong here.
"But when are you going to do that and at which club? What is your motivation? I try to get that thought process going."
Van de Beek's United record
Van de Beek has appeared in just 45 games across all competitions for United to date and has only two goals and two assists to his name.
The Netherlands international is still awaiting his first Premier League start of the current campaign, and it has been suggested that he could leave Old Trafford in the January transfer window.
Ten Hag addresses Ajax position amid Man Utd links
Van de Beek is now set to try and force his way back into the United team under their new interim boss Ralf Rangnick, who replaced Ole Gunnar Solskjaer last week.
The Red Devils are expected to appoint the Norwegian's permanent successor next summer and Ten Hag has been mentioned as a candidate.
The Ajax tactician added on the possibility of taking up a new role away from his homeland: "I think I'm ready for it. I would be happy to take up that challenge.
“But I'm not chasing it. If it turns out that that step will never come, I will not say that my coaching career has failed.
"But I think I have sufficient competencies to take on that challenge."