Erik ten Hag began the 2023-24 Premier League season without a recognised left-back, with Tyrell Malacia and Luke Shaw both sidelined due to injury.
The Red Devils brought in Sergio Reguilon on loan from Tottenham Hotspur as cover, but he returned to London in January, leaving the likes of Aaron Wan-Bissaka and Diogo Dalot to fill the void.
A year later the situation is not much better for Ten Hag's side, as they headed for their pre-season tour with Wan-Bissaka as the only senior full-back named in the squad.
Malacia appears to be still some way from returning to first-team action, while Dalot and Shaw are both entitled to a minimum three-week break following their participation in the Euro 2024 final.
Man United prioritise left-back signing this summer
According to The Mirror, defensive reinforcements are the main priority for Man United for the remainder of the transfer window, and the club has now created a three-man shortlist of players who they are considering making a move for this summer.
The report adds that the Red Devils wishlist of defenders includes former Chelsea left-back Marcos Alonso, who was not offered a contract extension at Barcelona and left as a free agent on June 30.
United were considering a move for the Spaniard at the start of last season but were unable to agree terms with the Catalans and moved on to Reguilon thereafter.
It is also understood that the club are keeping an eye on Crystal Palace defender Tyrick Mitchell, who could be acquired for less than his current market value given that he has entered the final 12 months of his deal at Selhurst Park.
Feyenoord's David Hancko, who can also play at centre-back, is believed to be the final name pencilled into the Red Devils' list of potential candidates.
Hancko's agent Branislav Jasurek stated in January that he was actively speaking to clubs about a move away from the Eredivisie for the 26-year-old Slovakia international.
Plenty of action still to come from Old Trafford this summer
While Man United have already splashed out £52m to sign Leny Yoro and a further £36m for striker Joshua Zirkzee, there is still plenty that could happen at Old Trafford before the transfer window slams shut.
The Red Devils are rumoured to be closing in on a deal for Paris Saint-Germain midfielder Manuel Ugarte, whose agent Jorge Mendes also represents Yoro. Mendes is believed to be keen on the Uruguayan international making the switch to the Premier League.
Additionally, United are believed to still be in contact with Bayern Munich centre-back Matthijs de Ligt, while adding a new right-back to the squad is also a possibility.
In terms of departures, reports in recent days suggest that Jadon Sancho could be headed to Ligue 1 with PSG despite burying the hatchet with Ten Hag upon returning from his loan spell with Borussia Dortmund.
Mason Greenwood and Donny van de Beek have already been moved on this summer, while Casemiro continues to be linked with a move to Saudi Arabia and a potential reunion with his former Real Madrid teammate Cristiano Ronaldo at Al-Nassr.