The England international has thrived in the Bundesliga since leaving Manchester City for Dortmund in 2017.
Ole Gunnar Solskjaer had identified Sancho as the key player in his overhaul at Old Trafford but their failure to qualify for the Champions League ended the club’s chances of landing the winger in the summer.
United remain interested in Sancho but now face competition from clubs in more attractive positions.
Heinrich insists the club want to keep Sancho for another 18 months, he admits it will be tough.
“Jadon can become one of the best players in Europe, or even the world,” Heinrich told Omnisport.
“It won’t be easy to keep him at Dortmund. We hope he plays one or two seasons longer but we all know very, very big clubs with a lot of money want to have him in their team.
“He should know Dortmund is an excellent place for young players to play consistently and to develop on a very, very high level.”