Place the uncooked wild rice, raw chicken, onion, celery, carrots, mushrooms, garlic, butter, chicken broth, and seasonings in crockpot. Stir to combine.
Cover and cook on LOW for 7-8 hours or HIGH 3-4 hours.
In the last 30 minutes of cook time, remove chicken from crockpot and shred with a fork.
Place shredded chicken back in crockpot.
Whisk together milk, greek yogurt and flour in a small bowl.
Slowly add in milk/yogurt/flour mixture.
Stir until well combined.
Place cover back on slow cooker and cook for an additional 20 minutes.