Reguilon, 23, spent last season on loan at Sevilla from Real Madrid, playing an integral part in their Europa League winning campaign.
And with Zinedine Zidane not yet prepared to use him at Real, the Spaniard looked highly likely to rejoin them on another season-long loan deal this summer.
United are also interested in signing Reguilon on a permanent basis, but Spanish outlet AS recently claimed his preference was to head back to Sevilla on loan and keep his dream of playing for Real alive.
Spending another year with Julen Lopetegui’s side would have allowed the left-back to gain more experience, improve as a player and hopefully impress Los Blancos boss Zidane.
Yet Sevilla have all but confirmed they will not be re-signing him this summer, instead completing a £9million deal to sign Acuna from Sporting Lisbon.
The Argentina international, 28, has put pen to paper on a four-year deal with Lopetegui’s side.
And that will come as a major relief to United, who are now in the driving seat to sign Reguilon.
The Red Devils could face competition from Premier League rivals Tottenham, yet being able to offer Champions League football this season gives them a major advantage.
If they do manage to sign Reguilon, though, United legend Rio Ferdinand doesn’t think his former club’s spending should stop there.
“I would say definitely after Van de Beek they need probably – if they’re going to really compete – three or four [signings]. Players that can go in and actually affect the first team, the first XI,” Ferdinand told BBC Radio 5 Live.
“And Reguilon we’re talking about, the lad at Sevilla who’s from Real Madrid, he was voted the best left-back in La Liga so really good credentials.
“Luke Shaw I think is unfortunate in terms of his injuries. He’s played games but then he hasn’t been able to sustain a full season without any injuries, which is disappointing.
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“But listen, if I was looking at it and looking at the team, in the forward areas I think one or two additions. One definitely, maybe two, are needed that can come in and affect that first team and push people, if not start.
“And then I think a centre-back. That area, for me, is where there’s a lack of real, genuine pace and I think the best teams around at the moment have a player in one of the two players that play [at centre-back] in a four that has genuine pace normally.”