Manchester United are reportedly unable to get a deal done for Porto's Alex Telles until they have sold the likes of Chris Smalling or Marcos Rojo.
United get their Premier League campaign underway on Saturday with a clash against Crystal Palace and new signing Donny van de Beek is expected to be involved.
But they have been frustrated in their efforts to add to Van de Beek's arrival, especially the pursuit of Borussia Dortmund's Jadon Sancho.
At left-back, United boss Ole Gunnar Solskjaer already has Luke Shaw and Brandon Williams but they made an approach for Real Madrid's Sergio Reguilon before Spurs hijacked the deal.
And United have now turned their attention to Telles, who is valued at around £17million.
However, according to Sky Sports, a deal for Telles is dependent on United offloading several fringe players.
Sky Sports News’ Kaveh Solhekol said on The Transfer Show: “We’ve been told Manchester United had preliminary discussions over a deal for Alex Telles and he could fit the bill if they decide to enter the market for a defender.
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“However, that could hinge on whether they are able to sell some players at the club, such as Chris Smalling or Marcos Rojo. At this stage, no deal has been agreed.”
After spending last season at Roma, Smalling is keen to return to Italy permanently.
While Rojo spent last season in Argentina with Estudiantes.
Speaking ahead of the match with Palace, Solskjaer insisted United are trying to add more quality to the squad.
"We're looking at a small pool of players who can add to the quality of our team and let's see what we can do. The club's working hard and I understand that they're working hard," he said.
"When we sit down and we discuss, sometimes it doesn't happen as planned. Life isn't a straight line here, sometimes things happen and I've always said it - I'm very happy to work with these players.
"There's still a few weeks left of the transfer window, it might happen that we get someone in. I've worked with the club and they know what I feel the team and the squad needs and let's see if we can add to what we have."