By Adam Shergold for MailOnline
Published: 08:23 BST, 5 August 2020 | Updated: 08:36 BST, 5 August 2020
It comes as United threaten to walk away from the deal if Dortmund, who are demanding £108million for the 20-year-old England winger, don't compromise with their asking price.
The Old Trafford club believe Dortmund are being unrealistic in their demands for Sancho given the current economic climate amid the Covid-19 pandemic.
Marco Lichtsteiner worked with Dortmund when they sold Aubameyang to Arsenal in 2018
The Swiss agent was also involved when Dortmund sold Ousmane Dembele to Barcelona
But Dortmund are determined one of their star assets won't be sold below their valuation and, according to German newspaper Bild, have enlisted the help of a man used in the Dembele and Aubameyang deals.
They report that agent Marco Lichtsteiner, the brother of former Arsenal and Juventus defender