The winger picked up a foot injury against Arsenal last weekend, when he left the stadium he was seen wearing a protective boot so the signs were bad.
Days later and United are still waiting to find out how bad the damage is but his foot is so swollen, it cannot be scanned at this stage.
However, the initial fears are that Nani has suffered a metatarsal injury and will be out of action until March which would be a massive blow to the club.