Louis van Gaal admits it will be "difficult" for Bastian Schweinsteiger to be fit for Euro 2016 after the Germany captain suffered a knee injury while away on international duty.
The Manchester United midfielder sustained a partial ligament tear in his right knee when training with the national team in preparation for last Saturday's friendly against England in Berlin.
With only eight Premier League games remaining, Schweinsteiger faces a race against time to return to action for his club before the end of the season.
The 31-year-old could also miss out on leading his country at the European Championship in France, with Germany kicking off their Group C campaign against Ukraine on June 12.
"It is a tragic injury because the expectation is not so good for him in respect of the European Championships, but you never know," Van Gaal told MUTV.
"I hope that he can reach that, but it shall be difficult.
"You can never say anything about that [missing the rest of the season] because he's started his rehabilitation. You have to wait and see."
Van Gaal was able to give a more positive update on the fitness of Wayne Rooney.
The England forward, who suffered a similar injury to Schweinsteiger back in February, is "doing great" according to his boss, with the plan for him to play for Manchester United's Under-21 side before making a first-team comeback.
There was also further good news over three other players in the squad - Ander Herrera, Ashley Young and long-term absentee Luke Shaw, who has been out since suffering a double fracture to his right leg in September.
"Ander Herrera and Ashley Young are coming back. Young and Adnan Januzaj played with the reserves in a match on the Friday of the international break. Luke Shaw will be back on the training pitch on Monday with the physio," the Dutchman added.