Manager Erik ten Hag is likely to be without his two senior specialist full-backs until November.
Luke Shaw recently joined his understudy Tyrell Malacia on the treatment table after sustaining a nasty muscular injury.
The Red Devils are now scrambling in search of a ready-made replacement as they look to fill the void ahead of the transfer window deadline on September 1.
Chelsea's Spanish left-back Marc Cucurella is one of the names being mentioned.
According to Marca, he wants to join Man United, amid negotiations between the two clubs.
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The 25-year-old became the world's most expensive left-back after joining Chelsea from Brighton in a £62million deal last summer.
Another option being considered is Brentford Rico Henry, who continues to star for the Bees.
He has been a prominent figure for Thomas Frank's side since his move from Walsall in 2016.
The 26-year-old missed just one Premier League game last campaign and has started all three of Brentford's games so far this term.
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Sergio Reguilon has also been linked with the vacant position, having been in the shadows ever since his £32m move to Spurs from Real Madrid in 2020.
Tottenham tried to offload the Spaniard last summer but had to settle for loaning him out to Atletico Madrid.
Though an injury-hit season meant Reguilon spent the majority of the campaign in Spain on the sidelines.
He remains out-of-favour under Ange Postecoglou, with Destiny Udogie and Ben Davies both ahead of him in the pecking order.
Barcelona's Marcos Alonso is the final name being considered by Ten Hag ahead of the transfer deadline.
The 32-year-old could seal a return to the Premier League after previously spending six years at Stamford Bridge.
According to ESPN, the player is happy in Catalonia, however, and has no intentions of moving back to England.
Alonso also started his side's match with Villarreal on Sunday, further highlighting how crucial he is to Xavi's plans.
The Spaniard signed a new deal in January, keeping him at Barcelona until next summer, and has a buyout clause of £43m.