The Portugal captain prepares for his Old Trafford home coming on Saturday.
During his first spell with the Red Devils, the 36-year-old scored 118 goals,
in 292 games over six successful years in the North West.
“I am capable,” Ronaldo told the club’s official website. “I am ready to go.”
United host Newcastle in the Premier League in a 15:00 BST kick-off.
The re-signing of Ronaldo for £12.8m from Juventus was one of the biggest transfer stories,
of the summer as United’s rivals Manchester City had looked to be one of the favourites to land the forward.
The Portuguese star, who will wear the number seven shirt once again,
won three Premier League titles, one Champions League, two League Cups and one FA Cup,
as well as the Fifa Club World Cup and Community Shield – under former manager Sir Alex Ferguson.
Although United have won trophies since Ronaldo left for Spanish giants Real Madrid in 2009,
they haven’t secured a top-flight title since the 2012-13 season.
“This is why I am here,” he said. “I am not here for a vacation.
“Before was good, winning important things and I wore the shirt before, many years ago, but I am here to win again.
“It is a good chance for me, for the supporters, for the club, to get one step ahead.
I am ready and I think I will be a huge thing in the next three or four years.”