Ralf Rangnick recommended Joško Gvardiol and Konrad Laimer to the Manchester United board before he left the club in the first week of manager Erik ten Hag's reign.
Former Red Bull sporting director Rangnick took over a United interim manager in December with a two-year consultancy role tagged on but departed following Ten Hag's arrival.
Rangnick regarded RB Leipzig and Croatia defender Gvardiol, 20, as a "must-buy" while Leipzig midfielder Laimer, 25, is generating interest from Bayern Munich.