There have been 16 different United players injured or ill already this campaign, with seven sidelined for Saturday’s Premier League home clash against Crystal Palace.
The Argentina defender sustained a fractured metatarsal in April’s Europa League quarter-final first leg against Sevilla, keeping him out for around two months.
Martinez is now understood to be looking at a similar timescale on the sidelines after United announced an issue with the same foot.
“Lisandro Martinez will be out of action for an extended period due to an aggravation of the foot injury he suffered in April,” the club said.
“The Argentinian defender experienced the setback in our Premier League game against Arsenal earlier this month.
“But it has now been determined that he needs a period on the sidelines for recovery and rehabilitation. Assessment is ongoing to decide next steps.”
Martinez’s absence in a gut punch for a United side that can welcome back Christian Eriksen and Scott McTominay after missing Tuesday’s 3-0 Carabao Cup win against Palace through illness.
“We did a proper diagnosis, in Argentina (on international duty) as well,” Ten Hag said of the absent defender.
“But now it came out that there was a problem. That’s very sad, first place of course for him but also the team because he wasn’t 100 per cent fit.
“I think it was a big difference, the Licha Martinez in the last games and, for instance, the Licha Martinez we have seen in the first season here at Manchester United.
“He will add to the team… not even add, he’s a really strong contributor to our levels and if already one player drops a level, then of course the team performance levels will be lower.”
Ten Hag recently admitted he was concerned about the number of injuries United have been picking up at a time when there are ever-increasing demands on elite players.
“Every time the shadow is expanding, and the load on the players is just too much” he said. “It’s such a great overload.
“But many colleagues have already pointed to that, and I have pointed to that as well.
“But it kept going, we keep expanding the shadow, but anywhere it will stop and players can’t deal any more with this overload.
— Manchester United (@ManUtd) September 29, 2023
“I think this is what you see across many squads in this moment.”
The strain of injuries and illness have been compounded by the absence of Antony and Jadon Sancho.
Antony has not played since the 3-1 loss at Arsenal on September 3, having been given a leave of absence to deal with allegations of abuse against him.
United announced on Friday that the winger will resume training and is available for selection again as he continues to co-operate with police inquiries.
But Antony will not feature against Palace this weekend, nor will Sancho.
Four weeks ago the England international claimed on social media that he had been made a “scapegoat” after Ten Hag said he left him out of the squad for the game at Arsenal because of poor performance in training.
United later announced Sancho was training “away from the first-team group, pending resolution of a squad discipline issue”.
Ten Hag has not backed down and gave short shrift to the latest questions about the banished winger.
“Many of you ask me so often these questions and I have said everything,” he said ahead of the Palace game.
When asked how long this situation with Sancho can continue, Ten Hag said curtly: “What I said – I said everything.”
Later pushed on the difference in handling of the Antony and Sancho situations, Ten Hag said: “Those issues are nothing to do with each other. Nothing. One is internal, the other one is external.”