The Portugal winger's Ferrari collided with a roadside barrier in a two-lane tunnel near Manchester Airport, writing off the vehicle, police said.
At the scene, the 23-year-old European player of the year gave a negative breath test to police officers, who said inquiries were ongoing to determine the cause of the crash.
"He's fine and is training as normal with the team this morning,'' the Manchester United team spokesman said.
The front of the red Ferrari was completely crushed after absorbing the impact of the crash. Metal debris, including the front left wheel, was scattered across the road.
"The Ferrari went straight into the wall, his front left hand wheel came off and then Ronaldo got out of the car," witness Jody Lomax told the BBC. "He was all right, he was walking - he was a bit shaken."
No other vehicles were involved, although United goalkeeper Edwin van der Sar was travelling behind Ronaldo in his Bentley at the time.