Ferguson must decide whether to start with the England man at the Jose Alvalade Stadium or persevere with Carlos Tevez, who is yet to score since his arrival at Old Trafford, or hand Louis Saha a recall.
"It is not an easy one because none of our three strikers are at 100% of the level you would want for European football," he said.
"Carlos is getting better but he will only reach the level we want by good training. We are trying to gauge Louis. He has been out for eight months, so the plan was to ease him in the way we are doing.
"And Wayne has only had one game, which is a month ago now.
"Basically, I have to decide whether to start with Wayne, or do what I did on Saturday by playing Carlos with Ryan Giggs and then bring Wayne and Louis off the bench. I want to get it right because I want to win the game."