Phil Jones came on for his team-mate after just 29 minutes. United's official Twitter account confirmed the blow:
Red Devils manager Jose Mourinho will be saddened to lose another central defender, having only just waved goodbye to Ivory Coast defender Eric Bailly as he jetted off for the 2017 Africa Cup of Nations.
The injury is poorly timed as far as United and Rojo are concerned, as Statman Dave painted a picture as to just how important the Argentina international has been in helping the club build their recent run of form:
There's also the matter of how this will affect United's winter transfer plans, particularly with Bailly having only just left for the AFCON, which promises to keep him out of United action for up to a month.
When asked about his January transfer plans on Friday, United manager Jose Mourinho said he would refrain from purchasing and instead trust the improved trio of Rojo, Chris Smalling and Phil Jones, per Mark Crellin of Sky Sports:
I hope the three can control the situation in those eight matches [that Bailly will miss at the Africa Cup of Nations].
I will try to rest one in every game. On Saturday [against Reading] I will rest one, against Hull [in Tuesday's EFL Cup semi-final first leg] another.
We'll try to make a rotation between these three. We still have Daley Blind as the fourth, in case we need him to play there. We have Michael Carrick. So let's try.
The manager will hope Rojo's injury doesn't cause too great a recovery setback, with the aforementioned Blind also able to step in at centre-back if required.
The Red Devils are entering a busy fixture period in which Rojo's services would be welcome, as they prepare to face Liverpool, Stoke City and Hull City (in both the league and League Cup), all before the end of January.