The best is rest. Don't ride the horse you will have to dress the ligament daily with a wrap and medicaine that will help it heal. keep the horse is a stall to where he can't go out and run and reinjure the ligament. Daily rest is a must just walk the horse around daily to get stronger.
There is a support wrap that may help alleviate the strain. Also there are supplements for various health concerns. I would try the breathe eze supplement. Some stall rest is good, but do not over do it. Let your horse tell you when he needs more exercise.
Avoid using the leg for a long time. Wrap with elastic leg bandages, and monitor circulation so the wrap is not overly tight. The horse should well be stalled during this time and avoid using excessive weight until healing completes.