Hi there! If this roast is raw, you must, must defrost it completely and safely. If you toss it in and cook from frozen., the center won't be safe though the meat may appear cooked and feel hot enough. Personally I don't like microwave defrosting, though if you have experience in doing it, go ahead. The safest defrosting is in the fridge but a roast would take probably at least overnight or even a full day to defrost completely. If it were me I'd do veggie fajitas instead and put the roast in the fridge to defrost for another dish in about 24 hours.
This is near and dear to my heart just now -- My daughter is in a science competiiton and one of her events is all about foodborne diseases, so we've learned a LOT about food handling and foodborne illnesses in recent months. What you describe -- putting frozen raw meat directly in a crock pot -- is exactly what no one should do. Thawing in a fridge and slowly is critical to ensuring the meat is ready to cook thoroughly.
Even if you put it in liquids like others are saying, by dinnertime tonight it will be really only defrosted, not truly cooked to a safe temperature for the correct amount of time at that temperature. The cooking takes place AFTER the defrosting is thoroughly done; the two things can't happen at the same time. You can't tell by looking or tasting whether meat is safe; only the right internal temperature for the right amount of time will definitely make it safe to eat. I just wouldn't chance it, knowing what I now know about food handling.