Manchester United don't need to convince Šeško to join them this season because Šeško has made it known to Leipzig and Newcastle United that he wishes to play for Manchester United, just the way Gyokeres made it known to Sporting CP and Manchester United that he wishes to play for Arsenal. The ball is now in Manchester United's court, and since Šeško wants to join Manchester United, the only thing that will stop Manchester United from signing Šeško from Leipzig is if Manchester United fails to meet Šeško's transfer fee.
It seems Manchester United will have to think more seriously about this if they want to bounce back next season. After such a poor season for themselves last season, at least Manchester United should be grateful that one of their players immediately wants to join the team, despite Manchester United's poor results last season. I hope Manchester United will pay the transfer fee for this player so that Manchester United's squad next season can be different and better than last season. Although I don't think Manchester United will be title contenders next season.