The 16-year-old is a regular in the Spanish Under-17 squad and is regarded as a huge prospect in international football.
United scouts have been tracking the youngster in recent weeks and are ready to make their move for Mongil.
“My idea is to go far in football and to play in the Primera Liga with Valladolid,” said Mongil.
“I know about the rumours, but I really have not spoken with any club.
“At the end of the season I will decide on any formal offers.”
