Grimaldo, 22, is a product of Barcelona's famed La Masia academy and was once tipped to be Jordi Alba's long-term successor at left-back at the Nou Camp. But since leaving his boyhood club in 2015, the Spaniard has grown into an integral member of the Benfica starting XI, impressing in his side's Champions League clash with United despite falling to a 1-0 defeat at the Estádio da Luz in October.
Shortly after that performance, Portuguese publication Record claimed Jose Mourinho had given his club the green light to intensify their scouting of the left-back and for them to step up their interest in the player ahead of a possible move.
United have already done business with Benfica this year, having signed Victor Lindelof from the Portuguese giants for a reported fee of £30m during the summer transfer window.
Benfica adopt a realistic stance when it comes to the subject of their prized assets leaving the club and while he stresses Grimaldo's situation remains the same as anyone else's at the club, Oliveira explains the Benfica model dictates that all players will ultimately have their price.
"All of the Benfica players have a certain market," Oliveira told IBTimes UK. "Now you have some differences, the oldest guy we have in the team is Julio Cesar who is 38 years old and youngest is Miles Svilar who is 18. The players with over 30 years, it is difficult to transfer them although for example Jonas, our best striker, when we hired him he was already 30.
"But for a player who is 25, 26, 27, or younger at 22, 23, 24, there is a huge market. I am not talking specifically about Grimaldo, but all players with those conditions, they have a market. We do not want to close the door to anyone. We don't want to force them to stay here. We want them to stay as long as they can. And while they are here they are happy, but once both parties agree on a transfer, usually the player leaves but as mentioned before, leave with a good relationship with the club."
United look increasingly likely to be in the market for a left-back with Luke Shaw's future at the club looking considerably bleak. Tottenham Hotspur's Danny Rose is another option for the club but Grimaldo provides an alternative option for Mourinho heading into the January transfer window.
Manchester City have also been credited with keen interest in the Spain Under-21 international with Pep Guardiola, who knows the player from his spell at the Nou Camp, impressed with his progress since moving to Portugal.
The Premier League leaders reportedly considered a January move for for the full-back until injury struck late last year, with the player revealing at the start of the summer his "pride" with being linked with a move to the Etihad Stadium and a reunion with his former manager.
City instead signed Benjamin Mendy for a club record fee but a season-ending knee injury has left Guardiola to consider bringing in a replacement in the New Year.
Domingos Oliveira was speaking at Web Summit Lisbon on behalf of S.L Benfica