The Argentina centre-back, 27, was carried off on a stretcher after his left knee buckled late in Sunday's 2-0 defeat by Crystal Palace at Old Trafford. "Manchester United can confirm that Lisandro Martinez suffered an injury to his cruciate ligament in Sunday's game against Crystal Palace," the club said in a statement.
"Assessment of the injury is ongoing to determine the appropriate course of treatment and the timescale for his rehabilitation. "Everyone at Manchester United wishes Lisandro Martinez strength for a successful recovery and we will be supporting him every step of the way."
United boss Ruben Amorim said after Palace match that he thought it was a "serious situation", adding: "Licha is really important for us, not just as a football player but the character he has, especially in this hard moment."