Bastian Schweinsteiger suffered his latest knee injury KO playing an innocuous pass in Germany's training session in Berlin and it's put his season in serious doubt.
It could mean another lengthy spell on the sidelines for United's 31-year-old midfielder as Schweinsteiger's national manager Joachim Low says the problem is "likely" to be the same knee injury that kept him out of 13 matches for the Reds.
The fact that it is the same ligament he tore against Sheffield United in the FA Cup in January- missing two months for United- will be a major concern for manager Louis van Gaal during the run-in.
Schweinsteiger is having an MRI scan to detect the full extent of the injury.
"He was injured at the end of the training session without any other involvement, while playing a square pass.
"It is likely to be the ligament which he had injured earlier in the season, he is being checked out in Munich at the moment so we do not know an exact diagnosis but it does not look positive."
Germany captain Schweinsteiger picked up the injury in training in Berlin on Tuesday ahead of his side's friendly with England, and has travelled to Munich with the German team doctor Hans-Wilhelm Mueller-Wohlfahrt.
Schweinsteiger, United's summer signing from Bundesliga champions Bayern came on as a second half sub in the Reds last four games as he regained match fitness following his absence since January's third round win against the Blades.
Schweinsteiger will miss both the world champions upcoming games with England and Italy.
No further information was given on the length of his lay-off, but he is likely to miss much of the remainder of the season and his participation in this summer's Euros could be in doubt.
Schweinsteiger had only just returned from a knee injury that had kept him out since January 9th.
He previously suffered a groin problem in October and was unable to start United's first three matches of the season due to a lack of match fitness having also picked up a knock on the pre-season tour of the USA.