It means United are facing a race against time to submit their own proposal and snatch Sesko from under the noses of their Premier League rivals.
They have reportedly been hit with a second transfer blow concerning their interest in Valencia youngster Javi Guerra. He has been linked with the Red Devils throughout the window but now seems likely to remain in his current surroundings.
Guerra is close to agreeing a new contract with Valencia, according to Marca, following a lengthy period of negotiations. They are said to view the midfielder as a star of the future and have made it a priority to extend his current deal.
The proposal on the table would reportedly keep him at the Mestalla until the summer of 2029 and include a major salary increase. The report adds that Guerra is eager to continue his development at Valencia despite the speculation over a potential exit.
As a result, it seems United will be forced to shelve their interest and turn to other targets if they want to improve their midfield this summer.
Ruben Amorim has confirmed that he is seeking certain traits from potential new players, saying: "We are always looking to improve the team and we have some characteristics that we would like to have, but again, it depends on the market."
Last month, the Portuguese manager explained: "I think our club in the moment, we need to be really careful when we sign a player. If we have to start the season with this squad, I'm happy because all the players that are here want to be here."
United have already signed three players since the end of last season, with the Red Devils taking steps to improve their attacking threat.
They kicked off their summer business by signing Matheus Cunha from Wolves before finalising a move for Bryan Mbeumo, which followed a lengthy period of negotiations. United have also added teenage defender Diego Leon to their squad.
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