Arsenal reportedly had a scout in attendance for Benfica's 10-0 win over Nacional at the weekend, with Alex Grimaldo the subject of the Premier League club's interest.
Grimaldo has been linked with the likes of Atletico Madrid, Inter Milan, Napoli and Manchester City in recent months.
The former Spain Under-21 international came through the youth system at Barcelona, but left Camp Nou without making a first-team appearance and has since forged a successful career in Portugal.
According to A Bola, a representative from Arsenal watched Grimaldo in action during his team's thumping win over Nacional in Portugal's top flight, with the defender opening the scoring inside the first minute.
The 23-year-old, who has now scored six times and registered five assists from left-back this season, will see his current deal with Benfica expire at the end of the 2020-21 campaign.