The 20-year-old has spent nearly a year with Bologna after he completed a move from Velez Sarsfield in the January transfer window.
After making eight appearances in the second half of last season, Castro has gone on to establish himself as a regular fixture in the Bologna side this term.
Castro has started 13 of his 14 Serie A matches this season, scoring four goals and contributing three assists.
The Argentina Under-23 international has also gained valuable European experience, having featured in the first five of Bologna's Champions League matches.
Arsenal learn Santiago Castro asking price
Castro's performances have caught the attention of Arsenal and Chelsea, who have sent scouts to monitor the striker's progress.
According to Caught Offside, Arsenal remain keen on the Bologna forward and have learnt what fee it could take to prise him away from Serie A.
The report claims that the Italian club would consider selling Castro for a fee in the region of €40m (£33m).
Castro may still be in the early stages of his career, but his potential could make him a shrewd investment for the Gunners.
Arsenal boss Mikel Arteta will be keen to add more depth to his centre-forward options, which currently consists of Kai Havertz and Gabriel Jesus.
Who could rival Arsenal for Santiago Castro?
However, the Gunners have a fight on their hands to secure Castro's services, with Aston Villa, Everton and Newcastle United all showing an interest.
Juventus and Inter Milan have also been linked with a move and could present Castro with the chance to stay in Serie A.
The Old Lady are on the lookout for a new striker due to the uncertainty surrounding Dusan Vlahovic's future at the Allianz Stadium.
Juventus boss Thiago Motta will be aware of Castro's ability after he worked with the Argentine before he left his role as Bologna head coach in the summer.
Meanwhile, Inter appear to view Castro as a potential successor to Lautaro Martinez once their talismanic striker decides to seek a fresh challenge in the future.
Written by
Ben Sully