Fitness concerns surround Manchester United defender Phil Jones after he left Old Trafford on crutches and with his foot in a protective boot on Monday.
Jones, 20, sustained an injury to his right ankle when challenging for the ball with Jobi McAnuff during United's FA Cup fifth round tie with Reading.
The England international was replaced by Nani, who went on to break the deadlock in the second half before Javier Hernandez scored as the Red Devils clinched a 2-1 victory over the Royals to set up a quarter-final with either Middlesbrough or Chelsea.
Jones was seen leaving the ground in discomfort, casting doubt over whether he will be available for United's Champions League last-16 second leg versus Real Madrid on March 5.
Sir Alex Ferguson told MUTV: "We will have to assess it in the morning. It is an ankle injury so I would imagine he would not be ready for Saturday and we will see what he is like after that."
The former Blackburn player impressed for the Red Devils during their first leg meeting with Real, keeping a close eye on Cristiano Ronaldo as the match ended in a 1-1 draw.
Manager Ferguson hailed his side for their all-round performance as they secured a last-eight tie with the winner of Chelsea's game with Middlesbrough.
"It was a good cup tie and ended up a really good one,'' he told ESPN. "They (Reading) went for it, piled the ball into the box and we withstood that. We played some great football, missed chances, had shots blocked and their goalkeeper made some saves.
"I`m satisfied with the quality of the game. We had to defend, our goalkeeper made some excellent saves because at 2-0 we were never comfortable.''