The Dutch centre-back has been sidelined since 30 November after suffering a lower back injury in United's 2-1 win over Crystal Palace. Although the problem was not initially considered serious, De Ligt has missed 15 consecutive matches in all competitions. That absence means he has sat out more games than the 14 appearances he has managed this season.
United are due to face Everton on Monday, 23 February, but De Ligt is regarded as a major doubt for that trip. He is now targeting a return in March.
Interim manager Michael Carrick has said the defender is improving but urged caution.
"Matta, we'll see how he develops," Carrick said. "The Everton game feels like a long time away at the moment, so we'll see. He's positive, he's moving in the right direction, but Mason is a little bit closer than him."
Earlier this month, Carrick said: "He's working his way back, taking good steps and improving. It's a little bit too soon at the moment but, hopefully, it won't be too long."
De Ligt has avoided surgery and has continued his rehabilitation at Carrington. However, a minor setback in late January delayed his comeback and he had not yet returned to full first-team training by mid-February.
In his absence, United have relied on the partnership of Harry Maguire and Lisandro Martínez at centre-back. The pair have helped United go unbeaten in five matches since Carrick's arrival in interim charge, bringing much-needed stability to the defence.
For De Ligt, the focus is now on completing his recovery without further setbacks. With March approaching, United are hopeful he will soon be available again as they look to maintain momentum in the weeks ahead.