The 25-year-old was forced to leave the field against Bournemouth earlier this month, after colliding with Marcos Senesi during our 3-0 win at Old Trafford.
Ten Hag later admitted that time would be needed to learn the full extent of Donny's injury, with the boss now revealing that the former Ajax midfielder now faces a lengthy period on the sidelines.
However, the manager was clear in his message to his fellow countryman, as he continues his recovery.
"I think it is quite positive news," Ten Hag told club media at Carrington.
"Of course, the bad news is he is out for the rest of the season, but the good news is, in the long term, his knee will be okay and he will be ready again to play at the highest levels and will be ready for the start of pre-season.