The Legally Blonde actress was struck by a vehicle driven by an 84-year-old woman as she went for a run in Santa Monica, California in September.
She escaped serious injury and shrugged the incident off as a minor mishap - but now she's revealed she landed on her head after being knocked down, and has been left with a scar on her forehead which she covers up with a new hairstyle.
Witherspoon tells U.K. chat show host Graham Norton, "I was jogging and I got hit by a car, it's not funny at all. They said I am very hard headed because I landed right on my head and I have a scar, hence my new hairdo. I don't remember much about it but miraculously and thank God I am fine."