The 21-year-old England striker has been out since sustaining a metatarsal in the opening day draw against Reading.
Boss Sir Alex Ferguson said: "Rooney has trained very well and will travel.
"But whether I start him, put him on the bench or leave him out until Wednesday night, that's something I have to decide."
He added: "He is desperate to play but we will take medical advice from the doctor."
Ferguson is delighted that Ronaldo is back at his disposal again - but warned him not to rise to any provocation in a manner that earned him a ban after his red card at Portsmouth.
He said: "Ronaldo being back is a big plus. You miss players who make a difference, who can change the pattern of a game and create opportunities for you.
"What happened at Portsmouth was unusual because he normally has a good temperament to handle that kind of thing.
"But there is no question some players will maybe try to provoke a reaction from him now.
"It is up to Ronaldo to control himself and to know what a good player he is. He is only helping other team by reacting to it."
Ferguson revealed Fletcher could face up to six weeks on the sidelines after a challenge by Patrick Vieira in Scotland's Euro 2008 win in Paris on Wednesday.
He said: "It is a disappointment. It was a really bad, nasty challenge."