Only De Jong has connections with Ajax doctors, but flights to Netherlands are expensive now and require quarantine.
It's the same as Umtiti, if everything was fine, he would be transparent and give an update to everyone on twitter or instagram, the situation is obviously bad...
He's going to ramp up his activity and try to train as if he's close to returning, basically at full intensity. If he suffers inflammation in the knee again and it doesn't go well he'll go for the surgery.
https://twitter.com/OnzeTv3/status/1375571358063673350