The 20-year-old is currently on loan at La Liga outfit Granada, making 14 appearances for the Spanish team during the 2023-24 campaign, including 13 outings in the league.
Fernandez has struggled to secure regular starts this term, but he played 88 minutes of Granada's 2-0 success over Cadiz in La Liga on Wednesday, which proved to be just the team's second league win of the season.
The defender also spent the 2022-23 campaign away from Old Trafford, representing Preston North End in the Championship, featuring on 42 occasions in all competitions.
Fernandez arrived at Man United from Real Madrid in 2020, and he has represented the Red Devils regularly at youth and Under-23s level, but the Spaniard is yet to make his first-team debut for the club.
Injuries to Tyrell Malacia and Luke Shaw led to claims that Fernandez would be given a run in the Man United side in the early stages of this season, but the club instead signed Sergio Reguilon on loan from Tottenham Hotspur as cover, with Fernandez being allowed to leave again on loan.
The left-back is out of contract this summer, though, and it is unclear whether he figures in the long-term plans of current head coach Erik ten Hag.
According to Record, Fernandez's form this season has caught the eye of Benfica, who are interested in signing him on a permanent basis this month.
The report claims that the Portuguese outfit have already been in touch with both Man United and Granada, and an offer of around €7m (£6m) could be presented to his parent club.
Fernandez's path into the first team at Old Trafford is blocked by Shaw, while Malacia will be the second-choice left-back once he has overcome a knee injury.
Man United are also said to be looking at bringing in another left-back this month, having ended Reguilon's loan spell at the club.
A recent report claimed that Girona's Miguel Gutierrez has been scouted by Ten Hag's side this season, with the Spaniard's performances for the overachievers drawing the attention of the Red Devils.
Shaw and Malacia are both currently on the sidelines through injury, with the former missing Man United's last two matches with an unspecified issue.
Ten Hag is said to be determined to add to his squad in January, and a loan departure for Donny van de Beek to Eintracht Frankfurt has already been confirmed, while Borussia Dortmund are expected to re-sign Jadon Sancho on loan despite the deal allegedly being delayed.