Nelson has been battling at Hoffenheim since the New Year.
"Reiss is the same as Jadon Sancho, he has the ability to play for an absolutely top club," said Jonker.
"I promised his mum in 2014 with all the changes in their life, I will take care of you and your family.
"In Arsenal there was no chance because it's about winning and those managers don't tackle the risk you might lose with a youngster.
"If you lose with your youngsters then there's a problem because it's your choice, you took the risk, you can always be criticised.
"That's difficult for boys like Jadon and Reiss to come through in England."