The defender – who ruptured the anterior cruciate ligament in his left knee in April – has returned to training.
Lejeune – who suffered the injury in April and had surgery in Italy – had only just returned from a tear of the anterior cruciate ligament in his right knee.
The 28-year-old, signed from Eibar two years ago by former manager Rafa Benitez, has been putting long hours in an attempt to return as soon as possible.
"He's quite incredible – a great pro,” said head coach Steve Bruce. “He's got one of them fancy cars like a batmobile, but you always see it. From the moment when I arrive to the moment I leave, he's always here. He's trained the last three or four days."