Casemiro pulled his hamstring in the Carabao Cup defeat to NewcastleCredit: Rex

Lisandro Martinez suffered a recurrence of his foot problem against Arsenal and needed another surgeryCredit: Richard Pelham / The Sun

Casemiro and Lisandro Martinez proved important stars in their debut season last term, firing United to two cup finals and third in the Premier League.

But both players will miss key parts of this campaign in crushing news for the Red Devils boss.

Casemiro pulled his hamstring against Newcastle last Wednesday and was initially only expected to be out for a few weeks.

But he could be sidelined for an extended period.

And Martinez’s ongoing foot problem, aggravated in September’s 3-1 defeat at Arsenal, required a second surgery of the year to force him out of action.

Now Ten Hag will be sweating on having them back in contention during the hectic festive period.

Speaking ahead of United’s Champions League clash at Copenhagen, the Dutchman said: “I have some time schedules, but it’s always difficult to expect that because they can have setbacks during rehab periods.

“Casemiro and Martinez are really strong injuries, I don’t expect them back before Christmas.”

Former United loanee Marcel Sabitzer identified Casemiro and Martinez as two of the three players who can get the club out of their current mess.

The Austrian said: “I feel sorry for them because they’re all good guys, and extremely hungry for success.

“Casemiro, Luke Shaw and Lisandro Martinez – they are leaders that provide structure and stability to the team.”

Ten Hag’s depleted Red Devils squad is also currently missing Tyrell Malacia, Luke Shaw and Amad Diallo through injury.

Jadon Sancho, meanwhile, remains out in the cold following his public spat with the manager.

Reports suggested United are considering a transfer swoop for Guido Rodriguez amid Casemiro’s injury woes.

The Real Betis ace won the World Cup with Argentina last year and could provide a suitable long-term option in midfield.

Erik ten Hag is without a number of important stars through injuryCredit: Rex

Casemiro and Martinez played a key part in United’s successful 2022-23 seasonCredit: Getty