It could also be something as simple as tendonitis, that is inflammation of a tendon. If it isn't contraindicated I would try to take an anti-inflammatory if that doesn't help within 5-7 days you should call your doctor for follow-up. An actual tear of the muscle would be excruciatingly painful so you would definitely know if that was the case, but a strained muscle could be the cause. You can also try applying ice twenty minutes on twenty minutes off for the first 24-48 hours.
