The Argentine hobbled off after just 18 minutes with an expression of clear annoyance and discomfort, walking straight down the tunnel whilst holding his shin-pad.
Phil Jones stepped in and enjoyed a relatively trouble free afternoon as Man United cruised to victory.
Mourinho, speaking after the game, was unable to shed light on the severity of the injury but confirmed that Rojo had suffered some sort of muscle related affliction.
“I don’t know I have to wait a little bit, a muscle is a muscle, we are always afraid of it. We will see,” said Mourinho.
“Without [Eric] Bailly, it will be so important for us to keep our defenders fit for January.”
Watching a player go down on his own accord is never a positive sign. And Rojo’s glum expression as he walked off failed to provide supporters with much assurance.
The best possible scenario, I guess, would be that Rojo – perhaps overworked following his exertions over December – has picked up a slight muscle strain, meaning an imminent return would be on the cards.
On the flip-side, this could be something like a pulled muscle – an affliction that requires an onslaught of physiotherapy. United fans will be desperate to see the in-form Argentine make an imminent return, preferably in time for the game against Liverpool on January 15.