His new club Wolfsburg play Man Utd tonight in the Champions League.
Obafemi Martins: "Even without Ronaldo and Tevez, I would say you face the same problems playing against United.
"In fact they are playing much better than before. When Ronaldo was on the pitch, everyone looked to him, expecting him to change the game when his team most needed it.
"But now United have a lot of players who can change a game, like Wayne Rooney, Michael Owen, Dimitar Berbatov. Even the defenders can score goals, so we must watch out for them all over the pitch.
"Rooney is playing so well at the moment - he can destroy defenders in an instant.
"He is scoring goals, maybe more goals than before, and he is helping the team in lots of other ways as well.
"He is a player we need to be very careful of."