The 20-year-old made his La Liga debut for Valencia late last season and has made 17 first-team appearances for the club in all.
Guerra has already scored four senior goals, including three this campaign – of which he has started the last four games for Ruben Baraja's side.
According to MARCA, Man United and Newcastle are sending scouts to watch every one of the Spain U21 international's matches.
However, in the event that either club does decide to try and sign him, he won't come cheap: his contract, which runs until 2027, contains a €100m (£86.7m) release clause.
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A versatile midfield operator who carries a significant attacking threat, Guerra has established himself as one of the most prodigious talents in La Liga.
He made his debut for Spain's U21 team earlier this month, featuring in European Under-21 Championship qualifiers against Malta and Scotland.
Having been promoted to Valencia's first-team squad this summer, Guerra began his 2023/24 season with a bang by coming off the bench to score an 88th-minute winner in a 2-1 victory away to Sevilla on the opening weekend.
He went on to find the net in an impressive 3-0 triumph over Atletico Madrid earlier this month, and in a 2-2 draw with Deportivo Alaves last time out.
More transfer stories
The next transfer window may be several months away, but transfer news continues to come thick and fast from around the Premier League and beyond.
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