Without an x-ray to ascertain a break in the bone your next best step may be to palpate the leg and feel for any abnormalities, even if you have to check a 'healthy' leg to compare any differences.
If you have a small cage, cat carrier, box, etc. then if you have to continue to keep him 'still', you can put him in that with all the bird's other normal amenities to help keep him quiet, still and rested... then you will have time to do more research in regards to possible splinting and or other palliative care...
I agree about putting the guinea in a small cage where it can't move around much. I have had a guinea and chickens with obviously broken legs and if they are kept off of it they will heal on their own. Vitamins, electrolytes and extra protein will help it to heal faster.
Thanks to everyone who replied. His leg is definitely broken so we're taking him to the vet today. Two days ago a friend checked it and splinted it. We tried to confine him in a box and a hammock but he got out. Right now he's in a small cage with hay and feathers on the floor. We are giving him plenty of meal worms and we'll look for vitamins and were going to make him a scrambled egg.