The Scotland Under-21 star has been impressive for Dundee United this season.
“Johnny will develop into a player but he is not ready to move on,” said Houston.
“He should stay here for another year to 18 months and then I won’t hold him back.
“He will attract interest. Celtic spoke to us in January about him but he is not ready for that yet.
“When he is ready, I will be the first to shake his hand and push him on. But he is still learning just now.
“He works hard but he also makes mistakes. He has lots to learn but in 18 months he will probably move on.”
