Manchester United striker stretchered off against Olympiakos.
The Dutchman was stretchered off late on, and as the game ended there was huge uncertainty as to the precise nature of the injury and potential impact for player and club.
David Moyes told SkySports after the game: "It doesn't look that bad, I've just gone into see him just now.
"He's got a knock around the knee area, having a look at him now. It could be a knee on the back of a knee, hopefully not serious."
The Scotsman went onto describe the striker's performance as fantastic, scoring all three goals as the Red Devils won 3-0.