The Red Devils were keen to add the young forward, who has impressed in pre-season with RB Salzburg.
However, the Austrian club are set to keep him for at least one more season.
According to transfer expert Fabrizio Romano, the Red Bull-owned club will do a deal with their sister team, RB Leipzig, who will likely sign Sesko next summer.
The Slovenia international is also happy to stay at Salzburg for his development for one more season.
He may not believe he is ready for a move to Manchester United yet.