The 22-year-old striker, who plays for the Barcelona B team, is contracted to the Catalan club until the summer of 2021, but has a release clause of €20m which can be triggered by interested clubs.
Arnaiz is highly rated by the Catalan club and he has been included in the first-team for all three of their Copa del Rey games by manager Ernesto Valverde this season. The Spanish forward has impressed every time he has been given the opportunity to score a goal in each of his appearances.
The Barcelona winger's latest exploits were during their first-leg last 16 draw against Celta Vigo and his goal on Thursday night created a record that even the great Lionel Messi did not achieve. Arnaiz became the first player in the club's history to score three goals in his first three shots on goal for the first-team and it came in just 133 minutes.
Arnaiz seems a shrewd capture after Barcelona moved to sign him last summer in a £3m (€3.3m) deal from Real Valladolid. However, according to Spanish publication Marca, if the left-winger, who can also play as a forward, continues to impress, interested suitors could easily prise him away from the Catalans if they activate his release clause.
Arsenal are not the only team monitoring the forward's progress with reports suggesting that Manchester United and Bayern Munich are also keen to sign the young winger. The Premier League duo are said to believe that his pace and ability to take on defenders will be an asset in the English top-flight, while the Bavarian giants are said to view him as a potential long-term replacement for French veteran Franck Ribery.