The Ecuador winger could also be forced to sit out the visit of another London side, Sam Allardyce's West Ham, on Wednesday night in the Reds' next Barclays Premier League assignment.
"He had a hip injury," the boss revealed to MUTV. "Just towards his back.
"He's had a bit of pain there for the last couple of weeks but he's been playing with it. That's the type of guy he is. He never mentioned it and plays on.
"All of a sudden, you ask him and he says: 'Yes, it's sore.'
"It won't be too long and he should be ready for maybe next week."