The Borussia Dortmund whiz has just made a winning debut for England against the Czech Republic.
"He's a huge talent, everybody knew that," said Jonker, whose most recent managerial job was with Wolfsburg. "In Germany he is confirming his huge talent, it's no surprise, you knew it.
"He needed that time to practise, to get the level, the power the strength and to handle the situation. He's being seen as some kind of sensation because he's just 18 years old and playing for Borussia Dortmund. Bayern Munich are interested, which is a huge thing. Just 18 years old and that good."