The Red Devils have four senior left-backs on their books, but Luke Shaw and Tyrell Malacia are currently both injured, while Alvaro Fernandez and Brandon Williams are out on loan.
Neither Fernandez nor Williams are believed to have futures at the club beyond this season, though, while there is thought to be concern when it comes to the long-term fitness of both Shaw and Malacia.
Shaw has been restricted to just 15 appearances in all competitions this season, and the England international is set to be out for the majority of the rest of the 2023-24 campaign due to a muscular problem.
The ex-Southampton youngster was missing between the middle of August and end of November due to injury, before spending more time out at the end of 2023 and start of 2024, and he then aggravated a muscular issue against Luton Town in the Premier League in the middle of last month.
Malacia, meanwhile, has not played a single minute of football this season due to a knee injury which has required two separate occasions.
The Netherlands international made 39 appearances for the Red Devils last season following a move from Feyenoord, but he has not been in a matchday squad in 2023-24, and Man United head coach Erik ten Hag has conceded that he is likely to miss the rest of the campaign.
"I think it's going to be difficult for him (Malacia) to be available this season. He will fight, he's back on the pitch, but not in the team and the process had some setbacks for him," Ten Hag told reporters.
"He's still going forwards really slowly, and the season is coming to an end."
Victor Lindelof is currently being used as a left-back, and the Sweden international is likely to be needed in that area for the rest of the campaign.
However, the return of Aaron Wan-Bissaka from injury, which could occur against Liverpool in the FA Cup next weekend, would open up the possibility of Diogo Dalot switching to left-back.
Man United had Sergio Reguilon on loan from Tottenham Hotspur in the first half of the season, but he was sent back to his parent club after Ten Hag was informed that Malacia would return in January.
According to Italian journalist Fabrizio Romano, the 20-time English champions are planning to move for a new left-back during the summer market, with a shortlist to be finalised in the near future.
Girona's Miguel Gutierrez has recently been linked with a switch to Old Trafford, although the Red Devils are likely to face competition for the Spaniard from both Real Madrid and Arsenal.
Los Blancos are believed have the option to re-sign Gutierrez for just €8m (£6.8m) during the upcoming summer transfer window, while his release clause for other clubs is said to be €35m (£29.8m).