Manchester United defender Chris Smalling is among the "top three centre-halves in the world", according to club captain Wayne Rooney.

Smalling, who has risen from a bit-part player to a first team regular under manager Louis van Gaal over the past 18 months, is enjoying his finest ever run of form for his club and has featured in all of United's games this season.

"He has been incredible and for me he is right up there in world football in terms of centre-halves," Rooney told the club's website (www.manutd.com).

"He is in the top three centre-halves in the world -- I think he is that good.

"He is a great player and he is developing to become more of a leader of the back four. It is great to see for both United and England, and hopefully that can continue for him and he can help us to be successful."

The England captain's praise of Smalling comes in the wake of Van Gaal saying the defender could one day captain United, and the 25-year-old has said the manager's influence has been key to his improved performances.

"When you hear such good praise, especially from Wazza (Rooney) and the manager, you just want to show them that it's not just words that are meaningless," Smalling said, quoted by the Telegraph.

"I think he (Van Gaal) is a very experienced manager. He says a lot of things that I try to take on board and I think he wants you to express yourself.

"When he shows that trust, I just want to repay it and do as well as I can. But yes, he has given me massive credit," he added.

Meanwhile, the club have announced that they will hold a testimonial for Rooney to mark his 12 years at Old Trafford and the striker has pledged to donate all the proceeds from the game to charity.

The match will be held at Old Trafford on Aug. 3, with the opponents yet to be decided and the funds generated will be distributed to several children's charities through the specifically created Wayne Rooney Foundation.

"The match night will obviously be special for me and my family but I hope that we can also deliver one or two surprises," Rooney said.