Manchester United forward Cristiano Ronaldo is capable of playing until he is 40 as he has adapted his playing style to extend his career, former captain Wayne Rooney said.

Ronaldo, 36, spent six seasons at Old Trafford between 2003 and 2009, winning eight major trophies, and rejoined United from Juventus last month on a two-year contract.

"The last time he played here, he was more of a runner, a great dribbler, with pace and power," said Rooney, now managing Derby County in the Championship.

"Whereas now, he's a goalscorer. I think his game has adapted dramatically."

Rooney, United's all-time top scorer, added that his former team-mate is a "completely different player" to the one that left the club 12 years ago but can still keep up with the physical demands of the Premier League.

"His ability is obviously one thing, but then he's also looked after himself massively... he's still in great condition. It wouldn't surprise me if he's playing until he's 40, like Ryan Giggs did, and still scoring goals."

"His team-mates will have to work a little harder. But if it's anything like last time - towards the last two years of playing with him - the team allowed him to do that because he scores you goals, and goals win you games."

Ronaldo, who scored 118 goals for United during his first spell, is expected to feature when they take on Newcastle in the Premier League on Saturday.