Solskjaer has been left concerned after seeing both Romelu Lukaku and Nemanja Matic return early from international duty.
Lukaku was released from the Belgium camp after undergoing an MRI scan on a foot injury.
Matic, meanwhile, was allowed to leave Serbia’s squad after picking up an undisclosed problem.
With Luke Shaw and Anthony Martial having already withdrawn from the England and France squads respectively, Alexis Sanchez also out and Marcus Rashford carrying an ankle injury, caretaker boss Solskjaer’s options are set to be stretched once again.
Matic played 86 minutes of United’s 2-1 FA Cup defeat to Wolves last Saturday, his second game in a row since returning from a four game absence through injury.
But Serbia coach Mladen Krstajic confirmed the midfielder was injured ahead of the friendly with Germany.
He said: “Nemanja Matic will not play in Wolfsburg, nor in Lisbon (against Portugal).
“He played the last match in the club, but did not stay in the field until the end.”
Matic was one of 10 United players sidelined by injury last month, which forced Solskjaer to call up youth players including James Garner, Angel Gomes, Tahith Chong and Mason Greenwood.
Although Matic missed United’s 0-0 draw at home to Liverpool and wins over Crystal Palace, Southampton and Paris Saint-Germain, he returned for the 2-0 defeat at Arsenal.
With Sanchez out for another month and Lukaku facing at least a week on the sidelines, Solskajer could face some big selection calls ahead of their end of season run-in.
United face Barcelona in the Champions League on April 10 and 16, as well as battling to secure a top-four place in the Premier League.
Their domestic run-in includes a derby clash against title-chasing neighbours Manchester City and top-four rivals Chelsea, both at Old Trafford.