John Wolffram says his 18-year-old Arabian, Rush, is recovering from claw and bite wounds, but the horse is expected to recover.
Wolffram wants to warn riders who are participating in the Tevis 100 mile horse race about the mountain lion.
The site of the attack was just 100 yards from the Western States Trail, the route of the internationally known wilderness riding event in which racers travel at night.
He says he wants riders to be aware of the attack so they can stay on alert while practicing for the race, and during the race itself, which takes place in three weeks.
Wolffram says there are known mountain lions in the area, but horses are not their usual food source. He says such encounters are just part of living in the foothills.