Sir Alex Ferguson has praised Wayne Rooney for helping to re-energise Manchester United when joining the club more than a decade ago.

The England international made a switch to Old Trafford from Everton for a fee of £30m as an 18-year-old in 2004 - a time when Ferguson's own future as Red Devils boss was up in the air.

Ahead of Rooney's testimonial against boyhood side Everton on Wednesday night, Ferguson has hailed the impact that the striker-cum-midfielder has made in the subsequent years at United.

"[Rooney] was an exciting signing. It was fairly shortly after I'd got rid of the idea of retiring and changed my mind, and I had to rethink about how we were going to take the club forward," he told United's official matchday programme.

"When you make the decision to retire, you stop thinking, but once I decided to stay I started thinking again and it was really centred around bringing energy back into the team by looking at young players. Of course there was Cristiano Ronaldo, then there was Rooney, and it was a fantastic period.

"The two of them were unbelievable. Wayne came in as a first-team player right away, even though he was only 18, and he's gone on to play for Manchester United for 12 years, which is very difficult in the present day. I always think that great players can play in any era. Bobby Charlton would have been a great player today and Wayne Rooney would have been a great player back then."

Rooney's testimonial to celebrate his 12 years' service to the club is expected to attract a crowd of around 60,000, with all profits going to charity.