Manchester United ace Wayne Rooney is unsure why he has suddenly hit a rich seam of scoring form.

The England hitman cannot quite put his finger on the transformation from a player effectively dropped by Sir Alex Ferguson for the home game against Bolton less than a month ago to the one that has now scored nine goals in seven games for club and country, including a well-taken effort in the demolition of Celtic at Old Trafford last night.

"I haven't got a clue what has changed," he said.

"I am starting to play a lot higher up the pitch and maybe I am attacking defenders a bit more than I was but the manager always allows you to attack players and create things in the opposition half. That has not changed.

"Obviously, when you score goals you get more confident and try different things. I am starting to run at defenders and commit them a bit more, so maybe that's it.

"I just know I was disappointed my goal ratio slipped from 23 to 18 last season, so I want to get it back into the 20s this season."