Nick Powell can use Cristiano Ronaldo as an inspiration to succeed at Manchester United, according to Crewe director of football Dario Gradi.

"It's a big step from our league to the Premier League, but Sir Alex Ferguson told him to accept the challenge," Gradi told BBC North West Tonight.

"He threw the challenge down to Ronaldo when he came as a kid, and Ronaldo rose to it, so why not [Powell]?"

Powell, 18, completed his transfer to Old Trafford on Tuesday.

BBC Radio Stoke reports an initial fee of £3m will be paid for the England Under-18 international, with the deal potentially rising to £6m depending on his success and appearances.

Portugal captain Ronaldo was also 18 when he joined United from Sporting Lisbon in 2003, and had six successful years at Old Trafford before his world-record £80m transfer to Real Madrid three summers ago.

Powell's wonder goal wows Wembley

And former Crewe boss Gradi, who gave a 16-year-old Powell his senior debut in August 2010, believes the teenager can take further heart from the progression of Alex Oxlade-Chamberlain.

The Arsenal youngster started for England in their opening group match of Euro 2012 against France on Monday, less than a year after helping Southampton win promotion from League One.

"[Oxlade-Chamberlain] is only a year or so older and probably not any more gifted, but obviously has shown that he can play in the Premier League, which Nick hasn't," said the 70-year-old, who was succeeded by Steve Davis as Alex manager in November.

Crewe-born teenager Powell scored 16 goals for the Alex last season, including a stunning 25-yard volley in the League Two play-off final victory over Cheltenham at Wembley last month.